Restraint stress depresses prolactin surges in pseudopregnant rats and adrenalectomy does not alter the response

Experiments were performed to determine whether restraint stress decreases the two prolactin (PRL) surges in pseudopregnant (PSP) rats in a manner similar to the stress-induced decrease of the proestrous PRL surge. Adrenal involvement as well as adaptation of the response was also investigated. Vaginal cycles were followed and animals exhibiting 2-3 normal cycles were cervically stimulated (CS) electromechanically to induce PSP. In one experiment the effect of adrenalectomy (ADX) on the nocturnal surge (NS) was investigated and was found to have no effect. In another set of experiments the effect of restraint stress was investigated. Immediately following an initial sample, the animals to be stressed had their hind legs tied together with plastic coated bell wire. Subsequent samples were taken for 3 hours. Restraint stress decreased the NS to 15% of the initial value within 30 minutes. ADX did not alter this response. Furthermore, 6-9 days of 3 hours of restraint stress did not attenuate the stress-induced decrease of the NS. Restraint stress also depressed the diurnal surge in PSP rats. These results indicate that restraint stress applied during the two PRL surges of PSP results in significant decreases in plasma PRL and that this response is not altered by ADX or by habituation to the stimulus.     

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.     

Pituitary prolactin concentrations associated with daily prolactin surges in pseudopregnant rats

During pseudopregnancy (PSP) two surges of prolactin (PRL) secretion from the pituitary are observed, the nocturnal surge at dawn and the diurnal surge in the evening. An attempt was made to clarify the correlation between changes in serum and pituitary PRL concentrations on day 5-6 of PSP. During the nocturnal surge, pituitary PRL concentration decreased significantly from 0000 hr to 0300-0600 hr. On the other hand, the high pituitary PRL concentration remained unchanged during the diurnal surge from 1200 hr to 1800 hr. These findings suggest that the nocturnal and diurnal PRL surges are regulated by separate controlling mechanisms.     

Effects of estradiol on the prolactin surges and the feedback mechanisms of gonadotropins in pseudopregnant rats

The influences of estradiol on the prolactin (PRL) surges and on the secretion of gonadotropins (LH and FSH) were investigated in the pseudopregnancy (PSP) of acutely ovariectomized rats. The four following experimental groups were prepared: 1) intact PSP as a control, 2) ovariectomy was performed on day 0 of PSP (OVX), 3) a Silastic tube containing estradiol was implanted for day 1-4 into the OVX rats (OVX-E 1-4), and 4) the Silastic tube was implanted for day 5-8 by the same manner into the OVX rats (OVX-E 5-8). In the OVX group nocturnal (N) PRL surges were observed at 0500 h on days 4, 8 and 12 examined, and increased secretions of LH and FSH were noted. In the OVX-E 1-4 group, the N PRL surge was suppressed on day 4, and the suppressed N PRL surge did not occur on day 8, after the removal of the implanted tubes. Diurnal (D) PRL surges with LH surges were observed at 1700 h on day 4 in these rats. Similarly, more remarkable results were obtained on days 8 and 12 in the OVX-E 5-8 group than in the OVX-E 1-4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Extrahypothalamic control of daily surges of prolactin secretion in pseudopregnant rat

The role of the limbic forebrain structures in controlling twice daily surges of prolactin (PRL) induced by cervical stimulation was investigated after acute or chronic deafferentation of the limbic forebrain afferents to the hypothalamus in rats. The preoptic area-roof section (POA-RS), which interrupted the rostral limbic afferents at the dorsal level of the anterior commissure, induced pseudopregnancy (PSP) and initiated the same nocturnal PRL surges as those initiated by the cervical stimulation. Diurnal PRL surges, however, did not occur following this procedure. The nocturnal PRL surge by POA-RS also occurred in ovariectomized rats. Deafferentation between the diagonal band of Broca and the medial preoptic area (F2-cut) initiated PSP in 37 % of the rats and induced an apparent but small nocturnal PRL surge. The rats with POA-RS or F2-cut showed restoration of their regular estrous cyclicities. Cervical stimulation after POA-RS did not affect the initiation of nocturnal PRL surge induced by POA-RS alone. POA-RS after cervical stimulation also did not affect the initiation of nocturnal PRL surge induced by cervical stimulation, though a diurnal PRL surge was initiated in these rats. The cut made just before the diagonal band of Broca after cervical stimulation did not inhibit the occurrence of either surge. Nocturnal and diurnal PRL surges were manifested after cervical stimulation in the rats with chronic POA-RS or F2-cut and their vaginal cyclicities were resumed. These results suggest that the limbic forebrain structures are not indispensable for the initiation of nocturnal PRL surges induced by cervical stimulation but may modify the hypothalamic mechanism(s) initiating a nocturnal PRL surge through the rostral part of the hypothalamus.     

Effect of restraint stress on prolactin and corticosterone levels in streptozotocin-induced diabetic rats

Changes in neuroendocrine function have been shown to occur in diabetic animals. The aim of the present study was to examine both the prolactin (PRL) and corticosterone (CORT) responses to a short period of restraint stress after the animals had been made diabetic for six weeks. The streptozotocin - induced diabetic rats had resting CORT levels which were significantly higher than the control animals. Acute restraint significantly increased CORT levels in both the control and diabetic rats. The CORT levels after stress were higher in the diabetic rats. However, the magnitude of the response (percent increase) was less in these animals. The resting PRL levels were not significantly different in the diabetic and control animals. The PRL levels significantly increased in both the control and diabetic rats when they were exposed to the restraint stress. The PRL levels after stress were significantly less in the diabetic rats, indicating a blunted PRL stress response. These results indicate that the diabetic state can affect an animals PRL and CORT response to a new acute stress.     

Turnover rates of hypothalamic dopamine associated with the two types of prolactin surges during pseudopregnancy in rats.

Two surges of prolactin (PRL) are observed daily during pseudopregnancy (PSP) in the rat: the nocturnal (N) surge at dawn and the diurnal (D) surge in the evening. In order to clarify differences in the controlling mechanisms of the two types of PRL surges, we attempted to examine the turnover rates of dopamine (DA) and norepinephrine (NE) in the preoptic-anterior hypothalamus (PAH) and mid-posterior hypothalamus (MPH) on day 5-6 of PSP. The turnover rates of DA in the hypothalamus were inversely correlated with the serum PRL levels at the D surge when a significant increase in serum PRL was accompanied by not only a marked decrease in turnover rates of DA in the PAH, but also a slight decrease in turnover rates of the amine in the MPH. Contrarily, no significant decrease occurred in the turnover rates of DA in the hypothalamus at the N surge. There was no obvious correlation between the turnover rates of NE in the hypothalamus and the serum PRL levels at either PRL surge. These findings suggest that decreased turnover rates of DA in the hypothalamus are involved in the D surge, and it is most probable that the N PRL surge occurs under the control of another factor such as the hypothalamic PRL-releasing factor.     

Replacement of progesterone restores the nocturnal surge of prolactin following suppression with a gonadotropin-releasing hormone agonist during early pregnancy in the rat

Continuous administration of a GnRH agonist (GnRH-Ag) at a dose of 5 micrograms/day, commencing on day 7 of pregnancy resulted in the suppression of daily nocturnal surges of prolactin (PRL) on day 8, and serum progesterone (P4) levels with subsequent termination of pregnancy. Replacement with dydrogesterone, a synthetic analog of P4 at a dose of 4 mg/day s.c. restored the magnitude of nocturnal PRL surges. These data suggest that GnRH-Ag may act either at the level of the brain to suppress the nocturnal PRL surge, resulting in a fall in serum P4 levels or at the level of the corpus luteum itself or at both sites simultaneously to terminate pregnancy.     

Servomechanism of prolactin and progesterone in regulating uterine gene expression

To investigate the interaction of PRL and progesterone in regulating uterine gene expression, we have quantitated the concentration of PRL receptor and of uteroglobin (UG) mRNA in the endometrium of rabbits of different ages and after treatment with different hormones. During uterine differentiation in 2- to 4-week old rabbits, a marked increase in unoccupied uterine PRL receptor number was observed, presumably increasing uterine sensitivity to PRL. Receptor values for 4-week old rabbits were comparable to values for sexually mature, estrous females, but were lower than in 5-day pseudopregnant (PSP) animals. When total PRL receptor was determined by Scatchard analysis after in vitro desaturation with MgCl2, PSP animals again expressed the highest receptor concentration with no changes in the dissociation constant (Kd) values. To determine whether progesterone regulates uterine PRL receptor, long term ovariectomized rabbits (greater than 12 weeks) were treated with various combinations of hormones, and unoccupied and total uterine PRL receptors were determined. Progesterone treatment resulted in the highest concentration of both unoccupied and total PRL receptor after desaturation and removal of anti-ovine PRL antibodies with MgCl2. The value for total uterine PRL receptor was equivalent to the value for mammary gland, and the Kd values (2-4 x 10(-10) M) were similar. Treatment of long term ovariectomized rabbits with progesterone, with or without estradiol, produced an increase (P less than 0.05) in the UG mRNA content, which also occurred in PSP animals. PRL alone had no effect on UG mRNA but PRL plus progesterone increased (P less than 0.05) UG mRNA in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)     

Study of the change of prolactin and progesterone during dopaminergic agonist treatments in pseudopregnant bitches

In order to clarify the role of prolactin (PRL) and progesterone (P(4)) in the pathophysiology of canine pseudopregnancy (PSP) we designed an experiment, where we induced an abrupt pharmacological blockade of PRL secretion with dopaminergic agonists (DA) or placebo (PL). Thirty overtly pseudopregnant (PSPT) bitches were randomly allocated to three groups of 10 animals each: PL, bromocriptine (BR), and cabergoline (CA), which were treated with PL, 7.5microg/kg BR and 5microg/kg CA, respectively. On days 1, 7 and 14 (day 0: beginning of the treatment) all the animals were classified into grades of intensity of PSP clinical signs, considering serum or milk secretion and enlargement of the mammary glands. Presence or absence of treatment side effects were recorded and blood samples for PRL and P(4) determinations collected. Serum PRL and P(4) concentrations (ng/ml) of all the animals on day 1 were (least squares means [LSM]+/-S.E.M.) 17.70+/-2.05 and 1.13+/-0.13, respectively. During the experiment, serum PRL and P(4) concentrations decreased (day effect, P<0.05). During the experiment, serum PRL concentrations were lower in the DA treated group (BR and CA) compared with PL group (P<0.05). After a week of treatment, the percentage change of PRL was -62.52 versus 102.16+/-46.20 (P<0.01) for the treated (BR and CA) and PL groups, respectively. Conversely, no significant differences were found in the percent change in PRL between the BR and the CA groups nor in P(4) percentage change among all groups for the same week. Significant differences in the achievement of complete remission between treated and PL groups were found on days 7 (40 versus 0%, P<0.05) and 14 (90 versus 0%, P<0.01). No significant correlation between PRL and P(4) was found on day 1 in any of the animals. However, a significant correlation for the same hormones was found on days 7 and 14 for the DA treated groups (r=0.46, P<0.01). While in the PL group, PRL concentrations and intensity of clinical signs were not significantly correlated on days 1, 7 and 14; in the DA treated groups they were significantly correlated on days 7 and 14 (r=0.34, P<0.05). The presence of a positive correlation between PRL concentrations and the grades of intensity of clinical signs in the treated animals indicates the major role of PRL in PSP physiopathology. However, the lack of correlation during spontaneous involution of PSP in the PL group demonstrates that PRL concentrations do not completely explain the problem. In summary, abrupt changes in serum PRL seemed to be more important in ceasing PSP signs than total PRL concentrations in these groups of animals.     

Prolactin secretion and its response to stress during the estrous cycle of the rats

Serum and pituitary prolactin (PRL) concentrations were measured during the estrous cycle of the rat with particular attention to the afternoons of the days of proestrus and estrus. Homogenizing machines, a Polytron and Sonifier, were used to extract PRL from the pituitary gland. The effects of ether anesthesia and restraint were also examined on the afternoons of both proestrus and estrus. The occurrence of a surge in PRL secretion during proestrus was confirmed with a peak at 1500 h, and this was accompanied by a decline in pituitary PRL content. A relatively high level of serum PRL was observed in the afternoon of estrus, during which time pituitary PRL content increased progressively. Ether anesthesia had no effect on the proestrus PRL surge, while restraint enhanced it. On the afternoon of estrus, restraint completely suppressed the rise in serum PRL, but ether anesthesia failed to suppress it completely. From these results, the following conclusions were drawn: 1) the PRL surge on the afternoon of proestrus occurs without synthesis of the hormone in the pituitary; 2) PRL secretion on the afternoon of estrus is accompanied by its synthesis in the gland; 3) the PRL response is distinct for each type of stress applied; and 4) PRL secretion is thus regulated by different mechanisms in proestrus and estrus.     

Mechanisms for the stimulatory effects of opioidergic and serotonergic input signals on prolactin in pregnant rats.

Dopamine (DA) neurons participate in tonic inhibition of prolactin (PRL), whereas beta-endorphin (beta-End) and serotonin (5-HT) neurons appear to be important stimulatory links for nocturnal PRL surges that occur throughout the first half of pregnancy in the rat. The purpose of this study was to determine how these neuronal components might be organized within the pathway controlling PRL release during gestation. Maximal stimulation of DA receptors with the agonist bromocriptine mesylate (Bromo) completely blocked the PRL response to beta-End (100 ng/microliters/min for 15 min) given intracerebroventricularly (i.c.v.) on day 8 of pregnancy. DA receptor blockade, produced by implanting a 25 mg pellet of haloperidol (Hal) on day 7 of pregnancy, resulted in PRL levels of 500-600 ng/ml by the following morning. beta-End i.c.v. or 250 mg/ml/kg BW of the DA synthesis inhibitor, alpha-methyl-p-tyrosine (alpha-MPT), given during the intersurge period, were equally effective in significantly increasing PRL (p less than 0.01) above pretreatment levels. beta-End and alpha-MPT evoked similar increases in rats pretreated with Hal, suggesting the stimulatory effect of beta-End on nocturnal PRL surges may primarily be due to DA inhibition. The next objective was to determine how beta-End and 5-HT might interact to stimulate the nocturnal surge. Day 8 pregnant rats were infused continuously with the opioid receptor blocker, naloxone hydrochloride (Nal), at a rate of 2.0 mg/10 min from 1000-1300 h. The PRL response to an injection of 20 mg/kg BW 5-hydroxytryptophan (5-HTP) at 1200 h was greatly attenuated, compared to controls infused with saline instead of Nal. This suggests that 5-HT stimulates PRL, at least in part, by an action at opioid receptors. Distilled H2O or 10 mg/kg BW of the selective S2 receptor blocker, ketanserin tartrate (Ket), was given intraperitoneally (i.p.) during the intersurge period on day 8 of pregnancy. All animals demonstrated an identical response to beta-End given 2 hours later, regardless of the type of pretreatment. It appears that beta-End does not stimulate PRL by way of an S2 receptor. Although beta-End induced a significant increase in PRL on day 16 of pregnancy, the response was attenuated by more than 60% compared to the response on day 8 of pregnancy. This attenuation may involve placental lactogens, shown to be secreted during this time and to inhibit PRL secretion.(ABSTRACT TRUNCATED AT 400 WORDS)     

The effect of restraint stress in early pregnancy in mice

Mice were exposed to 5 h of restraint stress on Days 1-3, 4-6, or 1-6 of pregnancy in the morning (08:30-13:30 h, a.m.) or afternoon (13:30-18:30 h, p.m.). Stress reduced the pregnancy rate from 90 to 52% (P less than 0.005) and average litter size on Day 18 from 8.2 to 5.2 young (P less than 0.005). Stress for 6 days was more effective than for 3 days (P less than 0.005) and an a.m. stress was more effective than a p.m. stress (P less than 0.005) in reducing the average litter size. Animals examined on Day 7 after 6 days of a.m. stress had decreased numbers of normal corpora lutea (CL), increased numbers of abnormal CL, decreased serum progesterone concentrations and tended to have fewer implantation sites. Abnormalities of embryo transport and implantation were also present. Changes in CL morphology and embryo transport and development were evident on Day 4 after only 3 days of restraint stress. These results show that many reproductive events of early pregnancy can be disrupted by restraint stress.     

Suppression of the prolactin surges in the pseudopregnant rat by urethane anesthesia

In pseudopregnancy of the rat prolactin (PRL) is released in the form of twice daily surges (nocturnal and diurnal surges). An attempt was made to examine the effects of urethane anesthesia on PRL surges during pseudopregnancy of the rat. In a preliminary study, using the continuous blood sampling method, the nocturnal PRL surge was completely blocked when urethane (1.0g/kg BW) was administered at 0:00 hr. Urethane (1.0g/kg BW) was injected at 0:00 or 12:00 hr, and serum and pituitary PRL concentrations were measured at 6:00 or 18:00 hr, respectively, to study the effects of urethane on nocturnal or diurnal PRL surges. There were no serum PRL surges during either the nocturnal or diurnal periods following urethane injection. The experiment examining pituitary PRL concentration at 6:00 or 18:00 hr confirmed that urethane (1.0g/kg) anesthesia suppressed the release of PRL surge from the pituitary.     

Stressor-associated alterations in porcine plasma prolactin

Experiments were conducted to determine effects of restraint and thermal stressors on plasma prolactin (PRL) in castrated male pigs. A single 20-min restraining period in a restraining cage which prevented both movement and injury increased (P less than 0.05) plasma PRL when applied at either 0800 or 1600 hr. Exposure to 32 degrees C at 0800-1000 hr or at 1600-1800 hr produced more moderate increases (P less than 0.05). A combination of 20 min restraint and 2 hr at 32 degrees C produced a response similar to restraint alone. Twenty minutes after stressor application plasma PRL concentrations in pigs exposed to restraint or restraint +32 degrees C at 1600 h were greater (P less than 0.05) than concentrations measured in all other treatment groups at that time interval. However, there were no statistically significant differences in additional quantitative indices of the plasma PRL responses (maximal level, maximal change, or integrated response above basal levels) among restraint, 32 degrees C, or restraint +32 degrees C, nor between morning and afternoon applications of treatment. Such data do not provide, therefore, any strong evidence for stressor-dependent or circadian differences in plasma PRL response. A second study subjected castrated male pigs to 20 degrees C (controls), 20 +/- 12 degrees C (cyclic temperature, sine wave variation), 5 degrees C constant, and 5 +/- 12 degrees C cyclic for 20 days. After 6 days exposure to 5 degrees C constant or 5 +/- 12 degrees C cyclic there were decreases (P less than 0.05) of 59 and 67% respectively in plasma PRL when compared either with pretreatment levels or with levels in pigs at 20 or 20 +/- 12 degrees C. There were no differences in PRL responses between cyclic vs constant temperatures. These results are the first to indicate that plasma PRL in pigs is affected by acute restraint and thermal stressors.     

Plasma progesterone and prolactin concentrations in overtly pseudopregnant bitches: a clinical study

Plasma concentrations of progesterone (P(4)) and prolactin (PRL) were measured in 35 bitches presented at veterinary clinics for symptoms of overt pseudopregnancy (PSP) between 50 and 95 days after the onset of proestrus. Results were compared to those from samples collected from 35 control bitches at comparable stages of the ovarian cycle (expressed as days after the onset of observed signs of proestrus). In the PSP bitches at 71.4+/-1.6 (mean+/-S.E.M.) days of the cycle, P(4) (1.5+/-0.2ng/mL) was lower (P<0.01) and PRL (16.0+/-1.9ng/mL) was higher (P<0.01), compared to P(4) (2.7+/-0.4ng/mL) and PRL (2.9+/-0.6ng/mL) in control bitches at 70.6+/-1.5 days of the cycle. Low P(4) was not a prerequisite for elevated PRL. Although elevated (> or =10ng/mL) PRL (20.9+/-2.0ng/mL) occurred more often with low (<2ng/mL) P(4) (20 of 24 cases) it also occurred with P(4) above 3ng/mL in two affected bitches and in two control bitches. Whether the occurrence of relatively low PRL concentrations (<4ng/mL) in samples obtained from 4 of the 35 pseudopregnant bitches reflected variable and often elevated PRL secretion or increased sensitivity to PRL in the absence of elevated prolactin in those animals was not determined. We inferred that elevated plasma PRL was often involved in the etiology of overt PSP; furthermore, a premature decline in circulating P(4) concentrations may be a factor in some instances.     

Light entrainment and stimulation of the secretion of prolactin in rams

Light entrainment and stimulation of PRL release were studied in rams submitted to artificial light regimes: In a first experiment four groups of animals were submitted to light regimes with a period of 6, 4, 3 or 2 months respectively (T6 to T2 groups) and amplitude of 8-16 h of daylength. In all four groups PRL level was significantly correlated with daylength (r greater than 0.51; P less than 0.01). However in July, when temperatures were indeed high, an additional PRL increase was observed in the T6, T4 and T3 groups, although the role of temperature appears debatable. In a second experiment, animals were exposed daily to 8 hrs. of light given in two photofractions. The first fraction of 7 hrs. began at the same time as "dawn", and the second of 1 hr ended at the same time as "dusk" of the T6 group in the first experiment which served as control group. Correlation of plasma prolactin in rams receiving 8 h light in one or two photofractions was highly significant (r = 0.66; P less than 0.001). This suggests that rams measured daylength between two limits considered as "dawn" and "dusk" even if lights were turned off during part of this interval.     

The physiology and mechanisms of the stress-induced changes in prolactin secretion in the rat

It is well known that stress in a number of forms induces the secretion of prolactin (PRL) in a number of species. What is not well known is that under certain conditions stress will also induce a decrease in PRL secretion. The conditions whereby stress decreases PRL are those where PRL secretion is elevated such as during the proestrous afternoon surge and during the nocturnal surge of pseudopregnancy. The physiologic significance of the stress-induced increase of PRL is suggested to be important in maintaining the competence of the immune system. The significance of the stress-induced decrease of PRL does not appear to have a major consequence on the physiology of reproduction in the rat and it is suggested that future studies be directed towards its significance in the immune system. The literature is reviewed dealing with the regulation of PRL secretion with emphasis on the factors that generate PRL surges in the rat. In addition the mechanism(s) of the stress-induced increase and decrease is (are) also examined. A hypothesis is presented suggesting an interaction between tuberoinfundibular dopamine secretion and a hypothalamic prolactin releasing factor in the generation of PRL surges and the differential effects of stress on PRL secretion.     

Postparturitional testosterone surge in male offspring of rats stressed and/or fed ethanol during late pregnancy

Male offspring of rats exposed to restraint stress and/or alcohol during late pregnancy show aberrant patterns of sexual behavior masculinization and defeminization that vary as a function of treatment. The impact of these treatments on the postparturitional testosterone (T) surge that contributes to sexual behavior differentiation was investigated. Plasma T was measured using radioimmunoassay in individual males sampled on day 21 of gestation within 10 min of cesarean delivery or 1, 2, or 4 h thereafter. Neonatal T in the group exposed only to stress did not differ from that in the control group. T was lower than control levels at birth in both alcohol groups. The magnitude of the T surge that occurred during the first hour of birth in the control group was diminished by 50% in both alcohol groups, whose T pattern was very similar. There was no common alteration in postparturitional T associated with the increased lordotic behavior potential that males in all three treatment groups typically share, nor were there idiosyncratic endocrine abnormalities linked to the very different male copulatory pattern each exhibits. Exposure to an abnormal T milieu during fetal as well as neonatal ontogeny may underlie the etiology of the different sexual behavior patterns exhibited by males exposed to stress and/or alcohol. Possible unique effects each treatment exerts on perinatal plasma T and it's aromatization to estradiol in hypothalamic targets are discussed.     

Effects of (-)-trans- delta 9-tetrahydrocannabinol on serum prolactin in the pseudopregnant rat

Groups of pseudopregnant rats were injected intravenously with (-)-trans- delta 9-tetrahydrocannabinol (THC) to determine its effects on serum prolactin (PRL) and the maintenance of pseudopregnancy. A single injection of 4 mg THC/kg BW at 2400 h on the first day of leukocytic vaginal smears of pseudopregnancy (D-1) delayed the ensuing nocturnal PRL surge for approximately one hour. When THC (1.0 mg/kg BW) was administered hourly from 2400 h on D-1 through 1700 h on D-2, the nocturnal surge was blocked and serum PRL levels were suppressed until 0600 h on D-2, but not thereafter. Neither treatment altered the duration of pseudopregnancy. These results indicate that the nocturnal surge secretion of PRL during early pseudopregnancy in the rat is sensitive to THC suppression, but that this suppression is not adequate to influence the duration of pseudopregnancy. The mechanism through which THC exerts this action remains unknown.