The reversible inhibition of steroid-induced sexual behavior by intracranial cycloheximide

Cycloheximide(Cyclo), an inhibitor of protein synthesis by a direct action on protein synthesis at the ribosomal level, was used to reversibly inhibit estrogen-induced sexual receptivity. Cyclo (100 μg per rat) was infused into the preoptic area(POA) of ovariectomized rats at varying times before, simultaneously with, and after 3 μg of subcutaneous estradiol benzoate (EB). All animals received 0.5 mg progesterone (P) 36 hr after EB, and were tested for sexual receptivity 4–6 hr after P. The females were placed with stud males and a lordosis quotient was computed for each female (lordosis quotient = number of lordosis responses/20 mounts by the male × 100). Females receiving Cyclo 6 hr before, simultaneously with, or 12 hr after EB showed significantly lower levels of sexual receptivity when compared to females receiving Cyclo 36 hr before and 18 and 24 hr after EB. When those animals that showed low levels of sexual behavior after Cyclo infusion were reprimed with EB and P 7 days later and presented with a male they showed high levels of sexual receptivity. Thus, the effect of Cyclo was reversible. Only Cyclo infusions into the POA (bilateral) and third ventricle were effective in suppressing sexual behavior. Caudate nucleus, lateral ventricle, and unilateral POA infusions were without effect.The data presented are in agreement with earlier work that utilized actinomycin D to inhibit steroid-induced sexual behavior. Cyclo was found to be less toxic than actinomycin D. All of the available evidence is consistent with the hypothesis that estrogen stimulates RNA and/or protein synthesis in its facilitation of sexual behavior in the female rat.     

Regulation of estrogen-stimulated lordosis behavior and hypothalamic progestin receptor induction by antiestrogens in female rats

Two estrogen antagonists, CI-628 (CI) and tamoxifen (TX), were used to examine the relationship between estrogen priming of lordosis behavior and progestin receptor induction in the hypothalamus-preoptic area (HPOA) of ovariectomized female rats. Lordosis behavior was assessed by measuring lordosis quotients (LQ) in response to injection of 2 micrograms of estradiol benzoate (EB) followed 48 hr later by 500 micrograms of progesterone (P). Behavior testing began 4 hr after P injection. The effects of antiestrogens were assessed by injecting CI and TX (1-2 mg) from 0 to 48 hr prior to EB. Levels of cytosol progestin receptor in the HPOA were determined by quantifying the specific binding of 0.5 nM [3H]R5020 to cytosols from animals receiving the same EB and antiestrogen treatments used in behavioral testing. TX given concurrently with or CI given 2 hr before EB abolished both lordosis behavior and induction of HPOA progestin receptors. In contrast, CI given 12 hr prior to EB abolished lordosis but permitted a 95% elevation in the concentration of progestin binding sites in the HPOA. TX or CI given 48 hr before EB resulted in moderate levels of lordosis (mean LQs from 56 to 69) and induction of HPOA progestin receptors from 85 to 130% above noninjected controls. However, CI given 24 hr prior to EB produced less than a 40% increase in brain R5020 binding even though lordosis behavior was equivalent to that seen in the 48-hr animals (mean LQ = 53). These data indicate that the effects of antiestrogens on female sexual behavior and on the synthesis of brain progestin receptors depend on which antiestrogen is used and the time interval between administration of estrogen and antiestrogen. They also demonstrate that under some conditions estrogen induction of cytosol progestin receptors in the HPOA can be dissociated from estrogen priming of lordosis behavior in rats.     

Mu-, delta-, and kappa-opioid receptor agonists selectively modulate sexual behaviors in the female rat: differential dependence on progesterone.

Previous studies suggested that opioid receptor agonists infused into the lateral ventricles can inhibit (through mu receptors) or facilitate (through delta receptors) the lordosis behavior of ovariectomized (OVX) rats treated with estrogen and a low dose of progesterone. The present study investigated the behavioral and hormonal specificity of those effects using more selective opioid receptor agonists. Sexually experienced OVX rats were implanted stereotaxically with guide cannulae aimed at the right lateral ventricle. One group of rats was treated with estradiol benzoate (EB, 10 micrograms) 48 hr and progesterone (P, 250 micrograms) 4 hr before testing, whereas the other group was treated with EB alone. Rats were infused with different doses of the selective mu-receptor agonist DAMGO, the selective delta-receptor agonist DPDPE, or the selective kappa-receptor agonist U50-488. The females were placed with a sexually vigorous male in a bilevel chamber (Mendelson and Gorzalka, 1987) for three tests of sexual behavior, beginning 15, 30, and 60 min after each infusion. DAMGO reduced lordosis quotients and magnitudes significantly in rats treated with EB and P, but not in rats treated with EB alone. In contrast, DPDPE and U50-488H increased lordosis quotients and magnitudes significantly in both steroid-treatment groups. Surprisingly, measures of proceptivity, rejection responses, and level changes were not affected significantly by mu or kappa agonists, although proceptivity and rejection responses were affected by DPDPE treatment. These results suggest that the effects of lateral ventricular infusions of opioid receptor agonists on the sexual behavior of female rats are relatively specific to lordosis behavior. Moreover, the facilitation of lordosis behavior by delta- or kappa-receptor agonists is independent of progesterone treatment, whereas the inhibitory effect of mu-receptor agonists on lordosis behavior may require the presence of progesterone.     

Comparison of the effects of estradiol-17beta and the synthetic estrogen, RU-2858, on lordosis behavior in adult female rats and guinea pigs

Female sexual behavior (as assessed by lordosis responses) in adult ovariectomized guinea pigs and rats was measured after a single subcutaneous injection of either the synthetic estrogen RU-2858 or estradiol-17β (E) and a subsequent injection of progesterone (P). Thresholds for responsiveness to each estrogen were determined over a range of doses from 1 to 640 μg/kg of body weight. RU-2858 was able to stimulate lordosis at doses several times lower than E in both guinea pigs and rats. In general, guinea pigs were less sensitive to both estrogenic compounds than rats and were particularly insensitive to E. Approximately 40% of guinea pigs given RU-2858 displayed lordosis prior to P injection. Subsequent P injection did not greatly enhance the intensity of lordosis responses in these animals. These guinea pigs were also more sensitive than the remaining 60% of RU-2858-injected guinea pigs on several indexes of lordosis intensity (e.g., lordosis threshold, duration of heat, duration of individual lordosis responses). Rats did not respond behaviorally to RU-2858 without a subsequent P injection nearly as frequently as did guinea pigs. At the doses used in this study, E did not facilitate lordosis behavior in rats or guinea pigs in the absence of a subsequent P injection.     

Effect of DA1 receptor blockade with SCH 23390 on the renal response to electrical stimulation of the renal nerves

To evaluate the existence of functional renal dopaminergic innervation in the dog, we studied the effects of direct electrical stimulation of the renal nerves (RNS) with and without blockade of the dopamine receptor (DA1) that mediates the vasodilating and natriuretic response to intrarenal infusion of DA. Before infusion of the DA1 receptor antagonist, SCH 23390, RNS at 1 Hz did not change renal blood flow (RBF) but caused decreased urinary sodium excretion (-53 +/- 9%, P less than 0.01) and fractional excretion of sodium (-47 +/- 10%, P less than 0.01). Stimulation at 4 and 12 Hz elicited marked renal vasoconstriction (delta RBF = -37 +/- 12%, P less than 0.05 and -57 +/- 12%, P less than 0.01, respectively). When RNS (1 Hz) was performed during DA1 receptor blockade with SCH 23390, 0.5 microgram . kg-1 . min-1 iv, the responses were not different than those before SCh 23390 infusion (urinary sodium excretion: -54 +/- 7%, P less than 0.01 and fractional excretion of sodium: -46 +/- 5%, P less than 0.01). Renal vasoconstriction was also not influenced by SCH 23390 (delta RBF = -35 +/- 11%, P less than 0.05 during 4 Hz RNS and -58 +/- 12%, P less than 0.01 at 12 Hz RNS). Thus, the present study does not support the concept of functional dopaminergic innervation of the canine kidney.     

Rat uterine microbiochemistry: metabolic enzyme activities stimulated by 17-beta-estradiol are localized in epithelial cells

Lactate dehydrogenase (LDH; EC 1.1.1.27), citrate synthase (CS; EC 4.1.3.7), and beta-hydroxyacyl-CoA-dehydrogenase (beta-OH-acyl-CoA-DH; EC 1.1.1.35) activities were determined in each of the three major cell types of rat uterus, i.e., epithelial, stromal, and smooth muscle, using quantitative microanalytical techniques. Adult ovariectomized rats were treated with 17-beta-estradiol to determine the time course and dose response (0.025-50 micrograms/300-g rat) effect of estrogen on enzyme activity of each type of uterine cell. The use of "oil well" and enzyme-cycling microtechniques to determine the time course and the dose responses of enzyme activity changes required microassays involving 1595 microdissected single cell specimens. Estradiol treatment increased epithelial LDH, CS and beta-OH-acyl-CoA-DH activity but had no effect on these enzymes in the stroma or in smooth muscle cells. The estradiol-stimulated peak enzyme activities on Day 4 in the intervention group are compared with those in the ovariectomized rat controls as follows: LDH, 44.5 +/- 3.5 vs 22.3 +/- 3.9; CS, 3.5 +/- 0.2 vs 1.5 +/- 0.6; beta-OH-acyl-CoA-H, 3.5 +/- 0.32 vs 2.2 +/- 0.2 (mean +/- standard deviation; mol/kg/hr). Stromal cell activities (LDH, 7.4 +/- 1.0; CS, 1.2 +/- 0.2; beta-OH-acyl-CoA-DH, 0.9 +/- 0.1) were significantly lower than epithelial cell levels and were similar to smooth muscle levels. Therefore, even in the ovariectomized animal epithelial cells have markedly higher metabolic activity compared with adjacent cells. The enzyme activities are expressed as moles of substrate reacting per kilogram of dry weight per hour. All three enzymes exhibited a 17-beta-estradiol-induced dose response between 0.025-0.15 micrograms/300-g rat. The three enzymes studied all had similar response patterns to estrogen. The effect of estradiol was restricted to epithelial cells, with enzyme activities increasing to maximal levels after approximately 96 hr of hormone treatment. This study therefore not only confirms the specific and differential metabolic responses of uterine cells to estradiol treatment, but clearly demonstrates that marked metabolic differences exist between epithelial cells and stromal or smooth muscle uterine cells.     

Hysterectomy-induced facilitation of lordosis behavior in the rat

The present study investigated the effect of hysterectomy on hormone-induced lordosis behavior. Lordosis quotients (LQ) were measured in hysterectomized-ovariectomized (HO) and ovariectomized-sham hysterectomized (OSH) rats after several treatments including either estradiol benzoate (EB) alone or EB plus progesterone (P) 44 hr later. Testing consisted of placing the females with sexually active males 48 hr after EB. In Experiment 1, HO animals treated with 5 μg/kg EB and 0.5 mg P had significantly higher LQs than OSH animals; groups treated with 10 μg/kg plus P were not different. Experiment 2 showed that a single injection of 50 μg/kg EB resulted in equally high levels of receptivity in both groups. The LQs of HO animals injected with 3 μg/kg for 4 days did not differ from those of OSH animals; however, the administration of 0.5 mg P 24 hr after the fourth EB injection resulted in significantly higher LQs in the HO group (Experiment 3). In Experiment 4, HO rats injected with 5 μg/kg EB and 0.1 mg P 44 hr later displayed higher levels of lordosis behavior than OSH animals. It was concluded that hysterectomy facilitated the lordosis behavior of ovariectomized rats injected with both EB and P and that the mechanism for this potentiation remains to be determined.     

Estrogen potentiates vasopressin-induced contraction of female rat aorta by enhancing cyclooxygenase-2 and thromboxane function

To determine the roles of estrogen and constrictor prostanoids in vasopressin (VP)-induced contraction of female rat aorta, vascular reactivity to VP was determined in thoracic aortas of intact, ovariectomized, and ovariectomized + estrogen-replaced female rats in the presence of indomethacin (Indo), NS-398, SQ-29,548, or vehicle control. The effects of estrogen on vascular reactivity to the thromboxane A(2) analog U-46619 were also examined. Maximal contractile response to VP in intact female rats (5,567 +/- 276 mg/mg of aortic ring wt) was markedly attenuated by ovariectomy (2,485 +/- 394 mg; P < 0.001) and restored by estrogen replacement with 17beta-estradiol (5,059 +/- 194 mg; P > 0.1). Indo and NS-398 significantly attenuated maximal responses to VP in intact female rats to a similar extent [3,176 +/- 179 (P < 0.0001) and 3,258 +/- 152 mg (P < 0.0001), respectively]. Ovariectomy abolished and estrogen replacement restored the inhibitory effects of Indo, NS-398, and SQ-29,548. Contractile responses of rat aorta to U-46619 were significantly greater (P < 0.0001) in females (5,040 +/- 238 mg) than in males (3,679 +/- 96 mg). Ovariectomy markedly attenuated (3,923 +/- 84 mg; P < 0.01) and estrogen replacement restored (5,024 +/- 155 mg; P > 0.1) responses to U-46619 in female aortas. These data reveal that estrogen is an important regulator of the contractile responses of female rat aorta to VP, which appears to potentiate both cyclooxygenase-2 and constrictor prostanoid function in the vascular wall.     

17beta-estradiol prevents oxidative stress and decreases blood pressure in ovariectomized rats

In this study, we tested whether estrogen deficiency is associated with oxidative stress and decreased nitric oxide (NO) production, which could be responsible for an increased blood pressure in ovariectomized rats. Hemodynamic studies were performed on conscious, chronically instrumented rats. Chronic estrogen replacement on ovariectomized rats lowered blood pressure approximately 13 mmHg, from 119 +/- 3 mmHg in ovariectomized rats to 106 +/- 3 mmHg in ovariectomized-treated rats; it was also accompanied by an increase in cardiac index and vascular conductance, achieving hemodynamic values similar to those shown by sham-operated rats. N(G)-nitro-L-arginine methyl ester administration lowered significantly less the vascular conductance (0.14 +/- 0.01 vs. 0.22 +/- 0.03 and 0.26 +/- 0.01 ml. min(-1). mmHg(-1)/100 g; P < 0.05) in ovariectomized rats than in the sham-operated and estrogen-treated ovariectomized rats, respectively. Estrogen replacement prevented the lower plasma levels of nitrites/nitrates observed in ovariectomized rats. The lower plasma total antioxidant status and reduced thiol groups and the increase in plasma lipoperoxides presented in ovariectomized animals were reestablished with the estrogen treatment. These results show that estrogen administration decreases blood pressure and increases vascular conductance in ovariectomized rats. This effect may be related to an increase in NO synthesis and/or preventing oxidative stress, then improving endothelial function.     

Effect of changes in sodium intake on atrial natriuretic factor (ANF) and peptides derived from the N terminus of the ANF prohormone in the rat.

The purpose of the present study was to determine whether variations in salt intake would alter the plasma concentrations of atrial natriuretic factor and the N-terminal atrial natriuretic factor prohormone peptides proANF 1-98 and proANF 31-67. Two groups of rats were placed on different salt intakes for 1 week. The low salt group of rats was fed a diet providing less than 0.1 mM NaCl/day and given deionized water to drink. The normal salt group of rats was fed regular rat chow with deionized water to drink, providing them with approximately 2 mM NaCl/day. Plasma atrial natriuretic factor was 204 +/- 60 pg/ml (mean +/- SE) in normal salt rats and was significantly lower in the low salt group (44 +/- 13 pg/ml, P less than 0.01). ProANF 1-98 was also significantly higher in the normal salt group (635 +/- 47 pg/ml) compared with the low salt group (353 +/- 33 pg/ml, P less than 0.01). ProANF 31-67 was 123 +/- 21 pg/ml in the normal salt group and 59 +/- 12 pg/ml in the low salt group (P less than 0.05). Plasma renin activity in ng angiotensin l/ml/hr averaged 1.80 +/- 0.15 in the normal salt group of rats and was significantly higher in the low salt group of rats (5.66 +/- 1.07, P less than 0.05). These results suggest that atrial natriuretic factor and the atrial natriuretic factor prohormones may play a role in the physiological adjustments to low salt intake.     

Effects of elastase-induced emphysema on airway responsiveness to methacholine in rats

We examined the effects of elastase-induced emphysema on lung volumes, pulmonary mechanics, and airway responses to inhaled methacholine (MCh) of nine male Brown Norway rats. Measurements were made before and weekly for 4 wk after elastase in five rats. In four rats measurements were made before and at 3 wk after elastase; in these same animals the effects of changes in end-expiratory lung volume on the airway responses to MCh were evaluated before and after elastase. Airway responses were determined from peak pulmonary resistance (RL) calculated after 30-s aerosolizations of saline and doubling concentrations of MCh from 1 to 64 mg/ml. Porcine pancreatic elastase (1 IU/g) was administered intratracheally. Before elastase RL rose from 0.20 +/- 0.02 cmH2O.ml-1.s (mean +/- SE; n = 9) to 0.57 +/- 0.06 after MCh (64 mg/ml). A plateau was observed in the concentration-response curve. Static compliance and the maximum increase in RL (delta RL64) were significantly correlated (r = 0.799, P less than 0.01). Three weeks after elastase the maximal airway response to MCh was enhanced and no plateau was observed; delta RL64 was 0.78 +/- 0.07 cmH2O.ml-1.s, significantly higher than control delta RL64 (0.36 +/- 0.7, P less than 0.05). Before elastase, increase of end-expiratory lung volume to functional residual capacity + 1.56 ml (+/- 0.08 ml) significantly reduced RL at 64 mg MCh/ml from 0.62 +/- 0.05 cmH2O.ml-1.s to 0.50 +/- 0.03, P less than 0.05.(ABSTRACT TRUNCATED AT 250 WORDS)     

Facilitation of receptive behavior in estrogen-primed female rats by the anti-progestin, RU 486

The progestin receptor antagonist RU 38486 (henceforth referred to as RU 486) was tested for facilitative effects on female receptive behavior in ovariectomized Long-Evans rats primed with 2 micrograms estradiol benzoate (EB). RU 486 (0, 0.5, 1.6, or 5.0 mg) was administered 48 hr after estrogen priming. The lordosis quotient (LQ) and lordosis score (LS) were assessed 4 hr after RU 486 administration in a standardized test consisting of a 10-mount test by a stimulus male. A significant dose effect was found by both LQ and LS, with those subjects receiving 5 mg of RU 486 being significantly more receptive than vehicle control animals. Thus RU 486 acted as a weak progestin agonist under testing conditions typical for assessment of progestin facilitation of female sexual behavior in rats. Low levels of proceptive behavior (hops and darts) were seen in a minority of the tests, and did not vary systematically as a function of the dose of RU 486 administered. We also examined the effects of RU 486 given before progesterone (P) on receptivity in a blocking paradigm and confirmed previous reports that the antagonist significantly attenuates facilitation of sexual behavior when given in combination with P. A progestin receptor assay of the cytosols of the hypothalamus-preoptic area in estrogen-primed female rats treated with 5 mg RU 486 revealed a significantly greater depletion of available cytosolic P receptors than when rats were treated with a similarly facilitating dose of P (100 micrograms). The results suggest a possible dual mode of action for RU 486--a weak, receptor-mediated agonistic effect on sexual behavior when given alone to estrogen-primed rats, and a competitive blocking effect on receptivity when administered with P.     

Intestinal brush border calcium uptake in spontaneously hypertensive rats and their genetically matched WKY rats

The current studies were designed to characterize calcium transport by intestinal brush border membrane in the spontaneously hypertensive rat (SHR) and normotensive control, the Wistar-Kyoto (WKY) rat. The biochemical and functional purity of the intestinal brush border membranes in SHR and WKY rats was validated by marker enzymes and the ability to transiently transport D-glucose in the presence of Na+ gradient. Calcium transport into duodenal and jejunal vesicles represented a minor binding component and transmembrane movement as evident by initial rate studies, A23187 studies, and lanthanum displacement experiments. Initial rate and time course of calcium uptake was lower in SHR compared with WKY rats. Kinetic analysis of calcium uptake by the jejunum (total uptake minus binding component) showed a Vmax of 6.98 +/- 0.2 and 1.8 +/- 0.2 nmol/mg protein/7 sec in WKY rats and SHR, respectively (P less than 0.001), whereas Km values were 0.76 +/- 0.04 and 0.87 +/- 0.1 mM for WKY rats and SHR, respectively. Similar kinetic analysis of calcium uptake by the duodenal segments showed a Vmax of 10.3 +/- 0.8 and 2.8 +/- 0.2 nmol/mg protein/7 sec in WKY rats and SHR, respectively (P less than 0.01). Km values were 0.7 +/- 0.2 and 0.3 +/- 0.06 mM (P greater than 0.05). Vmax of calcium uptake in the 2-week-old rats (prehypertensive period) was 6.0 +/- 0.3 and 3.53 +/- 0.3 nmol/mg protein/7 sec in WKY rats and SHR, respectively (P less than 0.001), whereas Km values were 0.60 +/- 0.07 and 0.5 +/- 0.01 mM, respectively. These results suggest that calcium binding and uptake by duodenal and jejunal intestinal brush border membranes of SHR is significantly decreased compared with WKY rats. The decrease in transmembrane calcium uptake is secondary to decrease in Vmax and is present before the appearance of hypertension, implying a genetically determined defect in calcium uptake in intestinal brush border membranes of the SHR.     

Nighttime immunoreactive somatostatin content of the median eminence in hypo- and hyperthyroid rats

The median eminence content of immunoreactive somatostatin (IRS) was measured by radioimmunoassay in 107 male albino rats, who were either hypothyroid after surgical thyroidectomy (N = 38), hyperthyroid following a subcutaneous implant of 5 mg of L-thyroxine (N = 36), or otherwise untreated (N = 33). Thyroid function was assessed by determining plasma levels of T4 and TSH from trunk blood obtained at the time of decapitation. Subgroups of animals from the 3 groups were killed either before (1800 hr), during (2200, 0200, 0400 hr), or after the dark portion of their 14:10 LD photoperiod. Although no changes in median eminence IRS content were found throughout the period of study within any of the 3 groups, hypothyroid animals (297.23 +/- 13.47 ng per ME; 620.41 +/- 58 ng IRS/mg protein) had a significantly lower median eminence IRS concentration than untreated rats (355.86 +/- 16.55 ng of IRS per ME, P less than 0.01; 906.86 +/- 96.38 ng IRS/mg protein, P less than 0.05) and hyperthyroid animals (384.12 +/- 14.67 ng per ME, P less than 0.001; 874.1 +/- 104.5 ng IRS@mg protein, P less than 0.05). It is concluded, that the feedback of thyroid hormones on the hypothalamic-pituitary axis during thyroid hormone excess in vivo, contrary to what occurs in hypothyroidism, is probably independent of hypothalamic somatostatin.     

Long-term superfusion of rat pituitary cells: interaction of 17 beta-estradiol with pulses of gonadotropin-releasing hormone on luteinizing hormone release

In a series of four experiments, the temporal development of acute inhibitory and delayed stimulatory effects of 17 beta-estradiol (E) on luteinizing hormone (LH) release by superfused rat anterior pituitary cells pulsed with gonadotropin-releasing hormone (GnRH) was studied. Dispersed anterior pituitary cells from ovariectomized rats were cultured on Bio-Beads for 3 days and then placed in columns and superfused for up to 24 hr. During superfusion, the cells were exposed to GnRH pulses (3 X 10(-9) M, one 6-min pulse/hr). Cells treated with E (3 X 10(-10) M) either before (only 24 hr prior to superfusion) or before and during superfusion released significantly (P less than 0.05) more LH in response to the first few pulses of GnRH than cells treated with diluent. In contrast, cells treated with E only during superfusion initially released less GnRH-induced LH than cells treated with diluent. In a subsequent experiment, the inhibitory effect of E reached a maximum by 1.5 hr (P less than 0.01), and then gradually disappeared after 4.5 hr. Cells superfused simultaneously with E and fixed "low"-dose GnRH (5 X 10(-10) M) pulses did not exhibit enhanced LH responses with time to that dose of GnRH. However, E-superfused cells responded more than diluent-superfused cells to subsequent stimulation with a higher-dose GnRH pulse. Superfusion of cells with E for 16.5 hr in the absence of GnRH pulses also did not increase release of LH to low-dose (5 X 10(-10) M) pulses of GnRH, yet did cause a transitory increase to subsequent high-dose (10(-8) M) GnRH pulses. In conclusion, these results demonstrate the direct biphasic inhibitory then stimulatory effects of E on GnRH-induced LH release by superfused rat anterior pituitary cells. Expression of the stimulatory effect of E is related to the dose of GnRH.     

Duration of hormonal deprivation: influences on physiological and behavioral responsiveness to estradiol

A total of 54 ovariectomized female guinea pigs were divided into three groups and tested six times at 2-week intervals for their responsiveness to exogenous ovarian hormones (3 days of 4 micrograms/kg estradiol benzoate plus 1 day of 0.4 mg/kg progesterone) or control injections (0.2 ml oil vehicle). Two weeks after ovariectomy, treatment with estradiol significantly reduced food intake and body weight, and also produced vaginal membrane rupture in 98.1% of the females. When tested for sexual behavior at 4, 6, and 8 hr after the progesterone injection, 29 of the subjects (53.7%) displayed lordosis in response to manual stimulation. Twelve weeks after ovariectomy, the effects of estradiol on food intake, body weight, and vaginal membrane condition had not diminished. However, the overall proportion of females from which lordosis could be elicited declined to 27.8%. Biweekly injections of estradiol benzoate plus progesterone to one of the groups of females did not prevent this decline in the sexual response. Based on these results, it was concluded that the observed reduction in behavioral lordosis does not represent a general decline in the responsiveness of ovariectomized guinea pigs to estrogenic stimulation, but may involve changes in their responsiveness to progesterone or in other mechanisms more specifically associated with sexual behavior.     

Long-term prolactin exposure differentially stimulated the transcellular and solvent drag-induced calcium transport in the duodenum of ovariectomized rats

Prolactin, having been shown to stimulate transcellular active and solvent drag-induced calcium transport in the duodenum of female rats, was postulated to improve duodenal calcium transport in estrogen-deficient rats. The aim of the present study was, therefore, to demonstrate the effects of long-term prolactin exposure produced by anterior pituitary (AP) transplantation on the duodenal calcium transport in young (9-week-old) and adult (22-week-old) ovariectomized rats. We found that ovariectomy did not alter the transcellular active duodenal calcium transport in young and adult rats fed normal calcium diet (1.0% w/w Ca) but decreased the solvent drag-induced duodenal calcium transport from 75.50 +/- 10.12 to 55.75 +/- 4.77 nmol.hr(-1).cm(-2) (P < 0.05) only in adult rats. Long-term prolactin exposure stimulated the transcellular active calcium transport in young and adult AP-grafted ovariectomized rats fed with normal calcium diet by more than 2-fold from 7.56 +/- 0.79 to 16.54 +/- 2.05 (P < 0.001) and 9.78 +/- 0.72 to 15.99 +/- 1.75 (P < 0.001) nmol.hr(-1).cm(-2), respectively. However, only the solvent drag-induced duodenal calcium transport in young rats was enhanced by prolactin from 95.51 +/- 10.64 to 163.20 +/- 18.03 nmol.hr(-1).cm(-2) (P < 0.001) whereas that in adult rats still showed a decreased flux from 75.50 +/- 10.12 to 47.77 +/- 5.42 nmol.hr(-1).cm(-2) (P < 0.05). Because oral calcium supplement has been widely used to improve calcium balance in estrogen-deficient animals, the effect of a high-calcium diet (2.0% w/w Ca) was also investigated. The results showed that stimulatory action of long-term prolactin on the transcellular active duodenal calcium transport in both young and adult rats was diminished after being fed a high-calcium diet. The same diet also abolished prolactin-enhanced solvent drag-induced duodenal calcium transport in young and further decreased that in adult AP-grafted ovariectomized rats. We concluded that the solvent drag-induced duodenal calcium transport in adult rats was decreased after ovariectomy. Long-term prolactin exposure stimulated the transcellular active duodenal calcium transport in both young and adult rats whereas enhancing the solvent drag-induced duodenal calcium transport only in young rats. Effects of prolactin were abolished by a high-calcium diet.     

Induction of lordosis responsiveness by vaginal stimulation in rats is independent of anterior or posterior pituitary hormones

In a previous study, rats that initially did not show lordosis in response to palpation of the flanks and perineum started to show lordosis to this stimulus when tested 10 sec after brief vaginal stimulation and continued to show lordosis responsiveness for more than 3 hr. In the present study, we tested the possibility that this effect of vaginal stimulation is mediated by the release of pituitary hormones. Hypophysectomized rats showed the lordosis-activating effect of vaginal stimulation, and this effect persisted for more than 1 hr, similar to rats with intact pituitaries. Oxytocin (50 or 100 mU/rat) or vasopressin (100 mU/rat) injected systemically did not induce lordosis responding in ovariectomized rats that received either a single injection of estradiol benzoate (2 μg/Kg) or no hormonal treatment. However, these individuals subsequently showed the lordosis-activating effect of vaginal stimulation. The mechanism by which vaginal stimulation activates lordosis responsiveness thus appears to be due to some process other than release of pituitary hormones.     

Methysergide delays the decompensatory responses to severe hemorrhage by activating 5-HT(1A) receptors

Central administration of the serotonin receptor ligand methysergide delays the decompensatory response to hypotensive hemorrhage. This study was performed to determine the receptor subtype that mediates this effect. Lateral ventricular (LV) injection of methysergide (40 microg) delayed the hypotensive, bradycardic, and sympathoinhibitory responses to blood withdrawal (1.26 ml/min) in conscious rats. The response was quantified, in part, as the blood volume withdrawal that produced a 40-mmHg fall in blood pressure. The delayed hypotensive response produced by methysergide (8.2 +/- 0.2 vs. 5.6 +/- 0.2 ml, P < 0.01) was reversed by the 5-hydroxytryptamine (HT)(1A) antagonist WAY-100635 (30 microg iv: 6.7 +/- 0.4 ml, P < 0. 01; 100 microg iv: 5.6 +/- 0.1 ml, P < 0.01). LV injection of the 5-HT(1A) agonist (+)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) also delayed the hypotensive (10 microg: 8.6 +/- 0.3, P < 0.01; 20 microg: 9.2 +/- 0.3 ml, P < 0.01), bradycardic, and sympathoinhibitory responses to hemorrhage. WAY-100635 (10 microg iv) completely reversed the effects of 8-OH-DPAT (20 microg: 5.4 +/- 0.3 ml). Neither selective blockade of 5-HT(2) receptors nor stimulation of 5-HT(1B/1D) receptors had any effect on hemorrhage responses. These data indicate that methysergide stimulates 5-HT(1A) receptors to delay the decompensatory responses to hemorrhage.     

Plasma protein and blood volume restitution after hemorrhage in conscious pregnant and ovarian steroid-replaced rats

We have previously shown that both plasma protein restitution and plasma volume restitution are significantly enhanced in female rats hemorrhaged during the proestrus phase of the estrous cycle. Estradiol and progesterone levels are markedly elevated during proestrus and also increase during pregnancy. The present studies were therefore designed to determine whether the ability to restore plasma protein and blood volume after hemorrhage is augmented during pregnancy and by chronically elevated estradiol levels. The response to moderate hemorrhage (22-23% blood loss) was evaluated in conscious pregnant rats during early and midgestation and compared with that of virgin female rats studied during metestrus. At 22 h posthemorrhage, plasma volume had increased to greater than basal levels, and blood volume was restored to 93 +/- 1% (metestrus), 91 +/- 2% (early pregnancy), and 98 +/- 2% (midgestation) of control (P > 0.05). Animals hemorrhaged during metestrus or early pregnancy restored the same amount of protein to the plasma as had been removed, whereas those hemorrhaged during midgestation restored nearly 50% more plasma protein than had been removed (P < 0.01). In ovariectomized animals with chronic steroid replacement that maintained plasma progesterone at metestrus levels (15 +/- 2 ng/ml) but raised plasma estradiol to twofold that of midgestation (22 +/- 3 pg/ml), the blood volume and plasma protein restitution responses to hemorrhage did not differ from those of ovariectomized animals with no steroid replacement. In summary, posthemorrhage restoration of plasma protein content is significantly augmented during midgestation, but not during early pregnancy. This augmented response cannot be attributed to chronic elevation of plasma estradiol levels alone.