Effect of calcitonin on the prolactin surge of proestrus

The effect of calcitonin (CT) on the prolactin (PRL) surge of proestrus in rats was investigated under normal and perturbed lighting conditions. Salmon calcitonin (SCT) was injected i.p. on diestrus 2 or on proestrus, plasma PRL levels were measured by radioimmunoassay. SCT had no effect on the PRL surge under normal lighting conditions but it induced a small drop in PRL level measured on proestrus morning, 3 hours after CT injection. Animals submitted to perturbed light conditions had higher PRL levels than those kept under normal lighting. These data would indicate that for the female rats on proestrus the sensitivity to stress due to injection and blood sampling may be modulated by changing the photoperiod. SCT injection under these conditions may facilitate this destabilization in PRL level.     

Impairment of stress-induced secretion of prolactin during development: effects of adrenalectomy, TRH and sulpiride

Ontogeny of serum and anterior pituitary gland PRL contents was investigated. Pituitary PRL concentrations were found to be low in fetus by 19th day of gestation and to rise slowly after birth with no sex differences being apparent until day 30. Adult levels were reached in males on day 15, while in females they were reached beyond this stage. Serum PRL levels exhibited a similar developmental pattern. In adult rats ether stress stimulated basal serum PRL significantly, with maximum effect one minute after onset of stress. The same pattern was seen with immature animals of 15-20 and 30 days of age. In contrast, in 2 or 6 day-old neonates, serum PRL concentrations remained unaffected by stress. This lack of responsiveness suggests the existence of a transient impairment of lactotrophs to respond to stressful stimuli during postnatal life. Adrenalectomy increased PRL release in adult and newborn rats from day 15 onward and potentiated the response of lactotrophs. Moreover, after adrenalectomy, 6 day-old rats became sensitive to ether stress, while acute treatment with dexamethasone abolished completely this response. In adult or 15 day-old neonates administration of TRH or sulpiride resulted in a marked increase in serum PRL levels. However, at 6 days TRH did not affect resting serum PRL concentrations significantly, whereas sulpiride remained efficient. Moreover, at this age, dopamine inhibited stress-induced PRL release and reduced the stimulatory effect of sulpiride.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of tartrate thyrotropin-releasing hormone treatment on serum thyrotropin, free triiodothyronine, free thyroxine and prolactin levels in patients with spinocerebellar degeneration.

The aim of the present study was to investigate the pituitary-thyroid axis function during the long-term (30 days) intramuscular administration of 4 mg/day of thyrotropin-releasing hormone tartrate (TRH-T) in 15 patients with spinocerebellar degeneration. The study was performed as follows: (1) acute 4 mg TRH-T test with hourly prolactin (PRL) and thyroid-stimulating hormone (TSH) level evaluations for 6 h; (2) placebo; and (3) 4 mg/day of TRH-T administration for 30 days with TSH, PRL, and free T3 and T4 (FT3 and FT4) levels evaluated on days 1, 15 and 30. Hormone determination was performed just before and 1 h after placebo or TRH-T administration. The acute administration of TRH-T caused a sustained rise of TSH which lasted until the 6th hour and of PRL which declined after 1 h (p < 0.01). During placebo administration, no change of TSH, PRL, FT3 or FT4 was observed. On the 1st day of treatment, 1 h after the TRH-T injection, a significant increase of both TSH and PRL levels occurred (p < 0.01). As compared to the 1st day, a significant decrease of the TSH (p < 0.01) levels occurred on the 15th and 30th days before TRH-T: the TSH response to TRH-T administration was present although less than on the 1st day (p < 0.01). Moreover, throughout the whole period of treatment, no difference was recorded for PRL levels before or after TRH-T administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of testosterone metabolites on serum gonadotropin concentrations in immature male rats.

The ability of testosterone, androsterone, 5alpha-androstane-3alpha,17beta-diol, and 5alpha-androstane-3beta,17beta-diol to prevent the castration-induced rise in serum gonadotropin levels was investigated in immature male rats. Rats castrated at 30 days of age were treated once per day by subcutaneous injection of 12.5-100 mug of the steroid per 100 g body weight per day for 3 days, beginning on the day of castration. The animals were sacrificed 24 h after the last injection. Testosterone propionate, androsterone propionate, and 5alpha-androstane-3alpha,17beta-diol dipropionate were also tested at the approximate molar equivalent of 100 mug of the free alcohol form per 100 g body weight per day. Testosterone propionate and 5alpha-androstane-3alpha,17beta-diol were the only compounds tested that prevented the castration induced rise in luteinizing hormone (LH) concentrations. Testosterone propionate also inhibited the rise in follicle stimulating hormone (FSH) concentrations whereas 5alpha-androstane-3alpha,17beta-diol inhibited the rise in FSH in one but not in another experiment. These were the only compounds tested that affected serum FSH concentrations. The lower doses of testosterone tested significantly increased serum LH, but not FSH concentrations compared to castrate control animals. The highest dose tested partially inhibited the rise in serum LH concentrations. Both androsterone and androsterone propionate maintained ventral prostate weights. Although neither compound prevented the castration induced rise in serum LH, two groups receiving androsterone had serum LH concentrations significantly lower than the castrate control group. 5alpha-Androstane-3beta,17beta-diol and 5alpha-androstane-3alpha,17beta-diol dipropionate failed to maintain ventral prostate weights or prevent the rise in serum gonadotropin levels. These results indicate that 5alpha-androstane-3alpha,17beta-diol is capable of preventing the castration induced rise in serum LH concentrations in the immature male rat and thus may participate in the regulation of LH secretion in these animals.     

Gonadal steroids deficiency and prolactin response to a met-enkephalin analog in man

The aim of this study was to ascertain whether there is a correlation between gonadal steroids and opioid control of prolactin (PRL) secretion. Four castrated men, aged 18 to 24 years were submitted to intravenous injection of 250 ug of a met-enkephalin analog (D-Ala2-Mephe4-Met-(o)-ol-Enkephalin, FK 33824) (DAMME). In normal men DAMME injection was also performed on the 6th day after treatment with clomiphene citrate (CC) (200 mg/day for 5 days), a specific nonsteroidal estrogen receptor blocker. In castrated men and in normal men after CC treatment, there was a lower PRL response to DAMME than in controls (P less than 0.0005). These results suggest that gonadal steroid deficiency seems to cause a change in the opioid system and/or dopaminergic control of prolactin secretion.     

Effects of an LHRH agonist and gonadotropins on testicular prolactin receptors

Effects of administration of the LHRH agonist D-Leu6-LHRH ethylamide (LHRH-A), gonadotropin (PMS), and their interaction on testicular prolactin (PRL) receptor levels were investigated in rats. LHRH-A (2 micrograms/100 g body wt.) or saline was injected SC daily, and PMS (5 IU) injected every other day. In intact rats, the testicular PRL receptor levels were about 400 fmoles/testis after either 1 or 7 daily injections of saline. Administration of LHRH-A decreased PRL receptors to 12% of that of saline-injected control rats at day 1, and to 20% at day 2, and PRL receptor levels were partially restored to 55% at day 7. In hypophysectomized rats given daily injections of saline for 7 days PRL receptor levels were only 20% of those in saline-injected intact rats. Injections of LHRH-A in hypophysectomized animals did not further decrease PRL receptor numbers at this time. Administration of PMS to hypophysectomized rats for 7 days partially reversed the reduction of PRL receptors that occurred after hypophysectomy, to 46% of those in intact controls. Injections of LHRH-A into hypophysectomized. PMS-treated animals did not significantly alter PRL receptors on day 1 (117% of that of saline-injected, hypophysectomized, PMS-treated rats at day 1) or day 2 (96% of same-day controls), but decreased PRL receptors on day 7 to 102 fmoles/testis (55% of same-day controls). This latter concentration is nearly the same as that in saline-injected, 7-day hypophysectomized rats not treated with PMS. These findings suggest that: (1) the effects of LHRH-A on testicular PRL receptors differ depending on the presence or absence of gonadotropin, (2) gonadotropin, primarily FSH, maintains some population of testicular PRL receptors, and these gonadotropin-dependent PRL receptors are suppressed by direct action of LHRH-A upon the testes, and (3) there is a population of PRL receptors which is not affected by LHRH-A or gonadotropin.     

Prevention of implantation by [D-Trp6-LH-RH in the rat: comparative study with the effects of large doses of HCG on pregnancy.

Effect of large doses of [D-Trp6]-LH-RH and HCG on implantation of fertilized ova was examined in the rat. Subcutaneous administration of 6ug[D-Trp6]-LH-RH per day from days 1 to 5 of pregnancy by an implanted minipump completely prevented the implantation of fertilized ova associated with a dramatic reduction of plasma progesterone on days 4 and 8, with a slight reduction of estradiol on day 4. There was no balooning of the uterus in the exploratory laparatomy on days 8 and 14. Administration of 1000 U of HCG daily from days 1 to 5 partially prevented implantation and completely terminated gestation. However, plasma progesterone and estradiol levels did not differ from those in the control animals. Ovaries in the [D-Trp6]-LH-RH treated rats appeared to be the same in size as those of the control pregnant rats, whereas the ovaries of the HCG-treated rats were hypertrophied. The results suggest that [D-Trp6]-LH-RH prevents nidation through a mechanism different from that for the adverse effect of excess of HCG on pregnancy.     

Effect of Bromocryptine on hormones and milk secretion in Murrah buffaloes ( Bubalus bubalis)

An experiment was carried out on 10 advance pregnant Murrah buffaloes to determine the role of hormones in milk secretion around parturition. Experimental animals were administered with a single injection of bromocryptine, @ 100 μg/kg BW, for 5 days before expected calving, whereas control group buffaloes were injected with placebo injections. Blood samples collected before parturition (-5,-4,-3,-2,-1 days), on day of parturition (day-0) and on day 1, 2, 3, 4, 5, 10 and 15 post partum were analyzed for growth hormone (GH), insulin like growth factor-I (IGF-I) and prolactin (PRL) by radioimmunassay methods. Milk samples were collected daily for 5 days and on day 10 and 15 after parturition. Milk fat, protein, lactose, citric acid, non-esterified fatty acids (NEFAs) and somatic cell counts (SCCs) were determined in milk samples. Bromocryptine treatment significantly (P < 0.01) decreased pre partum PRL and increased GH levels (P < 0.01) on day of parturition in experimental buffaloes without influencing plasma IGF-I level. Milk yield was significantly lower (P < 0.01) in experimental than in control group. Further, effect of bromocryptine on milk yield was only for a week. Milk yield increased (P < 0.01) gradually and was similar to control group on day 15 post partum. Bromocryptine treatment significantly increased milk SCC (P < 0.01) and protein content (P < 0.01) but there was no effect of treatment on fat, lactose, citric acid, glucose, milk and plasma NEFA concentration. It was concluded that prepartum suppression of PRL by bromocryptine impairs milk secretion temporarily in ensuing lactation. The significant rise in GH level before parturition and on day of parturition suggests a role of it in milk secretion of buffaloes.     

Paradoxical acute hypercalcemic effect of salmon calcitonin in patients having Paget's disease of bone after treatment with dichloromethylene diphosphonate

The hypocalcemia following administration of calcitonin may be an index to disease activity in Paget's disease of bone. Therefore, we assessed the effect of a single injection of 100 MRC units of salmon calcitonin (SCT) on plasma calcium in 28 patients with active Paget's disease before and after 6 months of treatment with dichloromethylene diphosphonate (Cl2MDP) at a dose of 400 mg/day (3 patients), 800 mg/day (8 patients), 1.600 mg/day (9 patients) or 2.600 mg/day (8 patients). The mean SCT-induced hypocalcemia was reduced by Cl2MDP and there was a significant positive correlation between the decrease of serum calcium induced by SCT and bone resorption evaluated by the number of osteoclasts on bone biopsy taken in pagetic iliac crest. After Cl2MCP treatment, 5 patients manifested a paradoxical hypercalcemic response to SCT injection ranging from +0.3 mg/dl to +0.5 mg/dl, which was sustained over the 9 hours following injection. As these patients had a dramatic inhibition of bone resorption induced by Cl2 MDP, it is suggested that the hypercalcemic response to SCT might reflect persistence or exaggeration of the early hypercalcemic effect of CT which reportedly precedes the hypocalcemic response to SCT.     

Role of ubiquitin-proteasome-dependent proteolytic process in degradation of muscle protein from diabetic rabbits.

The activity of ATP, ubiquitin (Ub)-dependent proteases partially purified from skeletal muscle (psoas) from alloxan diabetic rabbits was determined at different periods of insulin deficiency. Two days after alloxan injection, no change was observed in the activity of ATP, Ub-dependent proteases, but this activity increased 3 and 5 days after diabetes induction, attaining 181% of control values on the 5th day. However, after this early rise, the activity of muscle ATP, Ub-dependent proteases decreased, returning to values that did not differ significantly from controls 7 and 10 days after alloxan injection. After 15 days, the activity of these proteases was 57% lower than in muscle from control rabbits. Both the initial increase and the subsequent fall in the activity of the enzymes were prevented by insulin treatment of alloxan diabetic rabbits. The data suggest that Ub-proteasome-dependent proteolysis have an important role in the control of muscle protein degradation and may be regulated by insulin.     

Inhibition by estrogen of autofeedback regulation of prolactin secretion

The effect of estradiol-17 beta (E2) on autofeedback regulation of prolactin (PRL) secretion was tested in ovariectomized rats after s.c. implantation of an (E2)-containing or empty silastic capsule, followed by i.v. injection of bovine PRL (b-PRL) or bovine serum albumin (BSA; 500 micrograms/100 g B.W.). Implantation of an E2 capsule (day 0), 2.5 mm or 5.0 mm in length, produced plasma E2 concentrations of 79 +/- 6 (9) and 140 +/- 8 pg/ml (8), respectively. Assay of PRL in plasma samples collected at 1 h intervals between 1100-1800 h on days 3, 4 and 5, after E2 capsule implantation showed a daily afternoon PRL surge. Empty capsule-treated rats did not show any afternoon PRL surge. Injection of b-PRL, but not BSA, at 1200 h on day 3 reduced basal PRL release both on days 3 and 4 in empty capsule-treated rats. In ovariectomized rats treated with a smaller E2 capsule (2.5 mm), b-PRL injection at 1200 h on day 3 reduced the amplitude of the afternoon surge of PRL and the total amount of PRL released on day 4. b-PRL, however, was ineffective in reducing PRL release in rats bearing the large E2 capsule (5.0 mm). These results suggest that high E2 levels in the blood can block the negative feedback action of PRL on PRL release.     

Prolactin levels in the western spotted skunk: changes during pre- and periimplantation and effects of melatonin and lesions to the anterior hypothalamus

Prolactin (PRL) is the primary pituitary hormone responsible for initiating increased function of the corpus luteum and blastocyst implantation in the western spotted skunk. Therefore, we have designed experiments to validate a PRL RIA, characterize the preimplantation profile in PRL secretion, and determine the effects of exogenous melatonin and lesions to the anterior hypothalamic area (AHA) on PRL secretion in the skunk. These objectives were investigated with a heterologous RIA using canine PRL standards and antiserum. Displacement curves of skunk pituitary extract and serum were parallel to the canine PRL standard curve. Growth hormone-releasing hormone injection did not cause a significant change in plasma PRL levels as detected by the assay (p = 0.74). Injection of pimozide increased and bromocriptine decreased plasma PRL levels (p less than 0.05). A seasonal trend in plasma PRL levels was observed during the preimplantation period, with mean concentrations ranging from 5 ng/ml during the period of short day length in January to 17.1 ng/ml during the long day photoperiod in early May. The average date of blastocyst implantation in this study was 2 May (n = 16). Silastic capsules containing melatonin (n = 5) significantly delayed both the seasonal rise in plasma PRL levels and the time of implantation (p less than 0.05) compared to controls with empty capsules (n = 4). Lesions to the AHA (AHAx, n = 5) eliminated these effects of melatonin on both the rise in PRL and time of implantation. PRL levels were highly correlated with progesterone levels (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in the stress response of prolactin in young and aged female rats

The drawing of blood by orbital sinus puncture (OSP) under ether anesthesia is known to produce a marked increase in serum prolactin (PRL levels in young cycling female rats. The effect of this stressful procedure on PRL release was compared in young and aged female rats. Nonstressed PRL levels were obtained from blood drawn by decapitation. Whereas OSP with a one-minute ether exposure induced a marked increase in PRL levels in young rats on all days of the estrus cycle, older cycling female rats on the day of diestrus -1 and aged rats exhibiting prolonged diestrus (PD) showed virtually no increase above nonstressed levels. However, increasing the ether exposure time to five minutes did produce a rise in PRL levels. Old cycling female rats on the day of estrus and aged rats exhibiting constant estrus (CE) did show a PRL increase comparable to that seen in young animals. Ovariectomy (OVX) completely abolished the stress response seen in aged CE rats. The response, though markedly decreased, was still present in young ovariectomized rats. These experiments show that the stress-induced rise in PRL promoted by OSP under either anesthesia is markedly diminished in aged rats exhibiting a diestrus state. The attenuated response seen in these rats is believed due to factors characteristic of the diestrous state of aging.     

Relationship between norepinephrine release in the hypothalamic paraventricular nucleus and circulating prolactin levels in the Siberian hamster: role of photoperiod and the pineal gland

The impact of norepinephrine (NE) and its metabolite, 3-methoxy4-hydroxyphenylglycol (MHPG), on circulating prolactin (PRL) was evaluated in the paraventricular region of the hypothalamus as a function of photoperiod and integrity of the pineal gland. In Experiment 1, whole tissue content of NE and MHPG was assessed in male and female hamsters that had been pinealectomized or sham-pinealectomized and exposed to long or short photoperiods for 5 weeks. The results revealed a marginal effect of photoperiod in males, but no overall effects of surgery. Because analysis of whole tissue content can be complicated by concurrent changes in synthesis and storage rates, Experiment 2 was conducted using microdialysis to assess extracellular levels of NE and MHPG in female hamsters. Pinealectomy completely prevented the short-day-induced suppression of luteinizing hormone, but it only partially prevented the effects of short days on PRL. Furthermore, both NE and MHPG levels were significantly elevated in short-day-exposed pinealectomized and sham-operated animals. These results suggest that NE release within the paraventricular nucleus inhibits the circulating PRL levels and is one mechanism by which direct photic information can influence the neuroendocrine axis independently of the pineal melatonin signal.     

Salmon calcitonin induces pituitary tumor in rats.

Calcitonin is widely used in the treatment of post-menopausal osteoporosis. The present study was designed to investigate the effects of salmon calcitonin (SCT) on the incidence of the pituitary tumors in Sprague-Dawley (SD) rats. Subcutaneous injections of SCT at a dose of 160 IU/kg/day for 6 months reduced body weight and induced one pituitary hyperplasia and three pituitary adenomas in 4 of 5 animals, while 5 controls did not show any changes. Prolactin-positive cells were located at the periphery of the affected pituitaries adjacent to the prolactin-negative adenomas. In addition, serum concentrations of prolactin and TSH were lower than in the controls, although serum calcium or LH levels were not significantly different from the controls. Among 7 animals treated with SCT for 6 months followed by no medication for another 6 months, 5 adenomas were detected, one of which had invasive growth toward the adjacent tissue, whereas only one adenoma was found in 9 controls. These results suggest that SCT administration at a high dose may induce the formation of pituitary adenoma, or may accelerate the development of spontaneous pituitary adenomas, some of which show frequent mitotic figures and invasive growth into the surrounding tissue, possibly resulting in malignant transformation. This indicates the need for caution in considering whether calcitonin injections into patients with osteoporosis as well as Paget's disease may induce such pituitary tumors.     

Effects of clomiphene citrate on the pituitary gland in chronically estrogenized rat

Effects of clomiphene citrate (clomiphene) on the pituitary gland of chronically estrogenized ovariectomized rats were investigated. Estradiol-17 beta (E2) pellet implanted subcutaneously in castrated rats for 7 days caused significant increases in pituitary weight and serum prolactin (PRL) level but suppressed serum luteinizing hormone (LH) level. In the estrogenized rats about 40% of estrogen receptor (ER) found in whole pituitary cells (65 +/- 7 fmol/10 mg tissue) was observed in the nucleus, while 60% of ER was present in the cytosol fraction. A single injection of 5 micrograms E2 translocated cytosol ER immediately to nuclear compartment; amounts of ER found in cytosol and nuclear fractions were 16 +/- 1 and 37 +/- 4 fmol/10 mg tissue, respectively, at 1 h. However, the distribution of ER returned to the pre-injection level within 4 h. In the non-estrogenized castrated rats, the nuclear retention of ER was significantly longer than that in the estrogenized rats. A single administration of 200 micrograms clomiphene in the estrogenized rats, on the other hand, increased nuclear ER gradually. Nuclear ER reached the peak level at 4 h (62 +/- 5 fmol/10 mg tissue) and the level remained almost unchanged for 24 h. Cytosol ER decreased and reached a nadir at 4 h (4.3 +/- 0.3 fmol), and the replenishment of cytosol ER could not be detected for 24 h. Similar patterns of cytosol and nuclear ER following the clomiphene injection were also found in the castrated rats. The clomiphene administration in the estrogenized rats resulted in a significant reduction of the pituitary weight 48 h after the administration. The present results seem to show the antiestrogenic action of clomiphene in the pituitary gland.     

Regulation of aromatase mRNA and estradiol biosynthesis in rat ovarian granulosa and luteal cells by prolactin

Regulation by PRL of aromatase (P450arom) mRNA and protein and estradiol (E) biosynthesis was examined in granulosa cells during early stages of luteinization in vitro and in vivo. PRL caused a dose-dependent (10-1000 ng/ml) decrease in P450arom mRNA and E biosynthesis (greater than 99%) in luteinized rat granulosa cells in vitro, even when the cells were cultured in the presence of insulin and hydrocortisone (hormones known to synergize with PRL to induce proteins in mammary tissue) or in the presence of forskolin (a nonhormonal stimulator of cAMP). PRL also prevented the marked increases in aromatase mRNA and E biosynthesis stimulated by FSH and forskolin in nonluteinized preovulatory granulosa cells in culture. These effects of PRL on granulosa cells in culture were specific for aromatase and were not observed for other proteins, such as cholesterol side-chain cleavage cytochrome P450 (P450scc) and alpha 2-macroglobulin. PRL also decreased P450arom mRNA and protein during the early stages of luteinization in vivo. PRL administered to rats beginning day 1 postovulation to mimic hormone release during pseudopregnancy reduced the progressive increase in P450arom mRNA occurring in corpora lutea on days 3-4 in ovulated rats not treated with PRL. CB 154, a dopamine agonist that inhibits pituitary release of PRL, caused P450arom mRNA and protein to decrease 50% if given to pregnant rats on days 8-10 of gestation, but increased P450arom mRNA and protein if given to pregnant rats on days 10-12 of gestation. These diverse effects of PRL in pregnancy suggest that placental factors may modify the response of luteal cells to PRL during gestation.(ABSTRACT TRUNCATED AT 250 WORDS)     

1,25-Dihydroxycholecalciferol effects on plasma calcitonin levels and calcitonin mRNA in normal or partially vitamin D-depleted rats

The physiological effect of 1,25-(OH)2D3 on the regulation of calcitonin (CT) secretion was studied by measuring plasma CT levels and CT mRNAs extracted from thyroid glands of normal (D+) or partially vitamin D-depleted rats (D-). In both groups, acute 1,25-(OH)2D3 administration of 0.1 microgram/kg b.w. yielded an early drop in plasma calcium concentrations (around 0.6-1 mg/dl) with a maximum decrease 15 min after treatment. In spite of this hypocalcemia, a significant rise in plasma CT levels was observed within 5 min in D+ animals and within 30 min in D- animals after injection of the vitamin D metabolite. Nevertheless, the increased CT secretion was not associated with a marked and sustained rise in CT mRNA levels measured by dot-blot hybridization or CT mRNA activity evaluated by translation assay. By contrast to the observations made previously using supra-physiological doses of the vitamin D metabolites, no clear-cut effect on CT mRNA levels was found with lower doses. If we hypothesized that 1,25-(OH)2D3 plays a physiological role in CT secretion, our results suggest that this rapid control could be exerted at a post-translational level may be via an increase in the cytoplasmic ionized calcium concentration of C-cells.     

The influence of blinding, olfactory bulbectomy and pinealectomy on plasma and anterior pituitary prolactin levels and on uterine and anterior pituitary weights in normal and neonatally androgenized rats

Lactating Sprague-Dawley rats had their litters adjusted to 8-10 pups on day 3 of lactation favoring females and some litters were injected with 1.25 mg of testosterone propionate to neonatally androgenize (NA) them. At 22-25 days of age both normal and NA animals were ovariectomized (OVX) and subjected to either sham olfactory bulbectomy (ANOS) + sham pinealectomy (PX), blinding (BLD) + ANOS or BLD + ANOS + pinealectomy (PX). At 13 weeks of age all animals were injected with 0.5 mg of polyestradiol phosphate. At 15 weeks of age the animals were fitted with atrial catheters and at 16 weeks of age blood samples (0.3 ml) were obtained every 3 hours over a 24 hour period. Uterine and anterior pituitary (AP) weights were recorded at sacrifice. Plasma and AP were assayed for prolactin (PRL) by RIA and AP were also assayed for PRL using the Nb2 lymphoma cell PRL bioassay. In both normal and NA animals, BLD + ANOS suppressed plasma PRL levels and PX partially prevented this response. Uterine weights were similar among groups while AP weights were significantly lower for sensory deprived animals. Anterior pituitaries extracted at pH 7.6 had a PRL concentration that was higher for the BLD + ANOS groups when estimated by either RIA or BA, a result that was not observed when the AP were extracted at pH 10.6. The amount of PRL extracted at pH 10.6 was twice that obtained at pH 7.6. Sensory deprived animals that were OVX prepubertally and administered estrogen as adults had a small but significant increase in mean plasma prolactin at 1700 hr. Both normal and NA animals responded in a similar manner to experimental manipulation.     

The lack of a physiologic effect of the stress-induced decrease of the proestrous prolactin surge in the rat

Experiments were performed to determine whether the restraint stress-induced decrease in the proestrous prolactin (PRL) surge blocked luteolysis of the corpora lutea (CL), affected ovulation, or prevented the induction of pregnancy/pseudopregnancy in the next cycle. In all experiments rats were either stressed on proestrus and estrus, administered daily sc injections of 1 mg/day of 2-Br-alpha-ergocryptine (CB-154) for 4 days starting on diestrus II or not treated. In one experiment animals were sampled on the afternoon of proestrus to determine the effect of restraint stress on plasma PRL values and sacrificed on the morning of proestrus in the next cycle. Ovaries were removed, weighed, fixed and examined for number of CL. Restraint stress resulted in a significant increase in ovarian weight when compared to controls; CB-154 resulted in significant increases in ovarian weight when compared to stress and control animals. However, only CB-154-treated animals had a significant increase in the number of CL when compared to controls. In another experiment, animals were sacrificed on estrus of the next cycle and the oviducts examined for the number of ova. There were no differences among groups. In the final experiment, animals were placed with males of proven fertility on proestrus of the next cycle and examined for evidence of sperm in the vaginal lavage and/or vaginal plugs. CB-154 prevented the induction of pregnancy or pseudopregnancy due to a carry over effect of the drug on PRL surges. Restraint stress had no significant effect on the induction of pregnancy or pseudopregnancy. We conclude that there is no physiological significance to the stress-induced decrease of the proestrous PRL surge with respect to ovarian function or fertility.