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PubMed1991

Attenuation of the suckling-induced prolactin release and the high afternoon oscillations of plasma prolactin secretion of lactating rats by antiserum to vasopressin.

To investigate the role of vasopressin in prolactin (PRL) release during lactation, vasopressin antiserum (VP-Ab) was administered to lactating rats, giving it intravenously 15 min before permitting their previously isolated pups to suckle or to continuously suckled rats. The suckling-induced rise in plasma PRL levels was significantly less in VP-Ab-treated mothers than in rats receiving a similar amount of normal rabbit serum (NRS). The inhibitory effect of VP-Ab could not be detected on the next day. Angiotensin II antiserum (AII-Ab) had no effect on plasma PRL response induced by suckling. VP-Ab given to continuously suckled rats reduced the high amplitude oscillation of PRL concentration observed in NRS-injected rats. A transient increase of water intake was detected on the day of VP-Ab treatment only, which provides direct evidence for at least partial neutralization of vasopressin in the circulation. These findings suggest that vasopressin released from the neural lobe of the pituitary gland is essential for the normal PRL secretory response induced by suckling and the episodic pattern of PRL release in continuously suckled mother rats. Furthermore, these results support the assumption that disturbance in the regulation of water and electrolyte balance at the level of the neuro-intermediate lobe of the pituitary gland may alter PRL secretion during lactation.

Angiotensin II↗

PubMed1994

Analysis of pituitary prolactin and adrenocortical response to ether, formalin or restraint in lactating rats: rise in corticosterone, but no increase in plasma prolactin levels after exposure to stress.

It is well established that stress causes a rise in plasma prolactin (PRL) levels of male or cycling female rats. In lactating animals, the pituitary PRL response to stress is not well understood. Therefore, the purpose of the present study was to analyze this question in lactating rats having low or elevated prestress plasma PRL levels. The animals were exposed to ether, formalin or restraint, and plasma PRL and corticosterone levels were determined. In mothers continually together with their pups, plasma PRL levels decreased significantly after exposure to ether vapor or injection of formalin under the skin. At the same time, both agents caused a significant rise in blood corticosterone concentrations. Lactating rats isolated for 4 h had very low levels of PRL before application of stress. However, neither formalin nor restraint caused any elevation in their plasma PRL levels although both interventions increased blood corticosterone concentrations. Lactating mothers receiving formalin after a 30-min suckling stimulus preceded by 4 h isolation did not show appreciable changes in pituitary PRL secretion following the administration of formalin. For information on the mechanism of the effect of stress on PRL, lactating rats were pretreated with the dopamine receptor antagonist domperidone (injecting 80 micrograms/kg body weight) or were adrenalectomized 7 days prior to exposure to stress. The very high levels of PRL caused by domperidone decreased markedly in animals subjected to restraint stress. Administration of formalin to adrenalectomized lactating rats continually together with their litter caused a slight immediate decrease, followed by a transitory elevation and a subsequent small second decrease in blood PRL concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗

PubMed1995

Prolactin-synthesizing and prolactin-releasing activity of fetal and early postnatal rat pituitaries: in vivo and in vitro studies using RIA, reverse hemolytic plaque assay and immunocytochemistry.

In vivo and in vitro prolactin (PRL)-synthesizing and PRL-releasing activity of fetal (days 12-22) and early postnatal (days 1-10 after birth) rat pituitaries were studied by means of radioimmunoassay (RIA), reverse hemolytic plaque assay and immunocytochemistry. Using RIA, PRL could first be detected, both in the pituitary and in the serum, on day 17 of fetal development. From this day on, pituitary PRL gradually increased, the rise was particularly marked during the postnatal period and became depressed for the first 10 days of postnatal life. On fetal day 18, 12-15% of monodispersed pituitary cells displayed PRL immunopositivity, but only 3-5% of PRL-positive cells were plaque-forming, i.e. released PRL. By the end of gestation 19-25% and on postnatal day 10 42-45% of all pituitary cells were PRL cells and 31-35 and 15-17% of PRL-positive cells, respectively released PRL. Both pre- and postnatal PRL cells in monolayers were insensitive to TRH treatment. Pituitary primordia immunocytochemically and radioimmunologically negative for PRL (13- to 14-day-old fetal) when placed in serum-free organ culture were able to synthesize and release PRL. Fetal pituitary exhibited a highly regular increasing pattern of daily PRL release during a 7-day-culture period. Data obtained both in vivo and in vitro did not exhibit any sex differences. The present findings are consistent with all those observations suggesting an early emergence of fetal rat pituitary lactotrophs. The in vitro results support the concept that Rathke's pouch cells have substantial degree of independence from extrapituitary regulatory actions in the expression and further progression of specific functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1980

Autofeedback of prolactin in cultured prolactin-secreting pituitary cells.

Cultured GH3 rat pituitary tumor cells which secrete prolactin (PRL) were used to study autoregulation of rat PRL (rPRL) secretion. Acute (1 h) release of rPRL by cells in monolayer culture was inhibited by ovine PRL (oPRL; 10(-7) and 10(-8) M). Intracellular rPRL accumulation was not inhibited by exogenous oPRL. No effect of oPRL was seen during long-term (12-day) incubation of cells with oPRL (10(-7) to 10(-9) M). oPRL exerts an acute suppressive effect on rPRL release at the cellular level, but does not inhibit rPRL synthesis or long-term release.

Animals↗

PubMed1985

Prolactin control of growth and prolactin autoregulation in cultured human pituitary cells.

A human pituitary cell line (18-54,SF) grows in serum-free medium and secretes prolactin (PRL). Autoregulation of pituitary cell growth and PRL production by exogenously supplied ovine PRL (oPRL) was investigated. Human PRL (hPRL) and oPRL stimulated pituitary cell growth up to 92% and 85%, respectively, at hPRL and oPRL additions of 100-1,000 ng/ml. Short-term (1 h) incubation of the cells with oPRL decreased hPRL secretion from the cells by 72% at 10 ng/ml addition. Intracellular hPRL was stimulated under the same conditions by 50-275% at oPRL concentrations of 10-1,000 ng/ml. Long-term (10 days) incubation of the cells with oPRL had no significant effect on extracellular or intracellular hPRL production. These data suggest that the pituitary gland can serve as a primary feedback site and that PRL can autoregulate its own production as well as affect the growth of pituitary cells.

Cell Division↗

PubMed1978

Loss of central nervous system component of dopaminergic inhibition of prolactin secretion in patients with prolactin-secreting pituitary tumors.

The administration of l-dopa suppresses prolactin (PRL) secretion in normal subjects and in patients with hyperprolactinemia, although it is not known whether this effect, which requires the conversion of dopa to dopamine, is mediated peripherally or through the central nervous system. To distinguish between these effects, 10 normal subjects (6 male, 4 female) and 8 patients with hyperprolactinemia associated with pituitary tumors were given l-dopa, 0.5 g alone, or 0.1 g after a 24-h pretreatment with carbidopa, 50 mg every 6 h, which produces peripheral dopa decarboxylase inhibition. Similar degrees of PRL suppression were observed in normal subjects (basal plasma PRL 13+/-2 ng/ml) after l-dopa alone (48+/-4%) and after l-dopa plus carbidopa (58+/-6%). In patients with pituitary tumors and elevated plasma PRL (73+/-14 ng/ml), l-dopa alone led to PRL suppression comparable with that in normal subjects (47+/-6%). However, l-dopa plus carbidopa resulted in only minimal suppression of plasma PRL (19+/-4%) which was significantly less than after l-dopa alone (P < 0.001). Urinary homovanillic acid excretion, which reflected peripheral dopa decarboxylation was similar in controls and tumor patients after l-dopa both alone and after carbidopa pretreatment. Comparable suppression of PRL levels in response to a dopamine infusion (4 mug/kg per min for 3 h) was observed in controls and tumor patients. The results indicate that although peripheral conversion of exogenous dopa to dopamine can suppress PRL secretion, in normals, the central nervous system conversion of dopa to dopamine in the presence of peripheral dopa decarboxylase inhibition is sufficient to account for its PRL-suppressive effects. In contrast, patients with tumors, while retaining peripheral dopaminergic inhibitory effects on PRL secretion, exhibit a marked reduction of central dopaminergic inhibition of PRL secretion.

Adult↗

PubMed1995

Prolactin and systemic lupus erythematosus: prolactin secretion by SLE lymphocytes and proliferative (autocrine) activity.

Accumulated evidence suggests that prolactin (PRL) is an important immunoregulator and might have a role in the pathogenesis of systemic lupus erythematosus (SLE). Moreover, a PRL-like molecule is secreted by normal human lymphocytes and acts as an autocrine growth factor for lymphoproliferation. The objective of this study was to explore the PRL-like peptide production by peripheral blood mononuclear cells (PBMC) from patients with SLE. We investigated the PRL secretion by PBMC from six female SLE patients and nine normal subjects (5 women and 4 men). Ficoll-Hypaque isolated PBMC (1 x 10(6) cells/ml) were cultured with and without maximal stimulatory doses of PHA (1 mg/ml) or PWM (1/200). At 72 h of culture supernatants were harvested and used to determine PRL immunoreactivity by a radioimmunoassay (NIDDK-reagents). Cell extracts and concentrated supernatants were prepared to determine PRL by Western blot analysis (NIDDK-reagents). SLE non-stimulated PBMC secreted significantly higher levels of PRL than normal non-stimulated PBMC (8.09 +/- 4.15 ng/ml vs. 3.48 +/- 2.36 ng/ml, P = 0.02 by Mann-Whitney test). High levels of PRL were secreted by SLE-PHA stimulated PBMC (6.88 +/- 4.53 ng/ml) and SLE-PWM stimulated PBMC (16.57 +/- 16.39 ng/ml) compared with normal-PHA stimulated PBMC (5.83 +/- 5.27 ng/ml) and normal-PWM stimulated PBMC (8.54 +/- 5.49 ng/ml), respectively, but the differences were not significant. The maximal production of PRL was found in PWM-stimulated lymphocytes in both groups. Cells extracts prepared from SLE non-stimulated and stimulated PBMC contained a 11 KDa PRL immunoreactive material. Concentrated supernatants from SLE non-stimulated and stimulated PBMC contained both a 11 KDa and a 24-27 KDa PRL immunoreactive material. Our data indicate that PBMC from patients with SLE have an increased production of PRL-like immunoreactive material. This PRL is released in vitro as two different molecular weight forms, and appears to be derived from B rather than T lymphocytes.

Adult↗

PubMed1991

Absence of pituitary prolactin epitopes in immunoreactive prolactin of rat brain.

Immunoreactive prolactin (ir-PRL) in rat brain has been consistently documented. However, the identity of this ir-PRL is controversial. Ir-PRL is defined by its ability to bind to PRL antibodies. All previous studies of brain ir-PRL have used polyclonal antibodies, at least one of which apparently crossreacts with a portion of the proopiomelanocortin molecule. To begin to define the epitopes comprising ir-PRL in the brain, we utilized two monoclonal antibodies (MAb) that recognize pituitary PRL in a variety of species, including rat. Immunocytochemistry was performed on rat brains and pituitary glands using two monoclonal and one polyclonal PRL antibody. Although both MAb immunostained lactotrophs of the rat pituitary gland, neither antibody immunostained cell bodies or neuronal processes in the brain. However, the polyclonal antiserum immunostained lactotrophs and a system of neuronal cell bodies and processes in the brain. Thus, epitopes found in pituitary PRL from several species are not found in ir-PRL in rat brain.

Animals↗

PubMed2004

Osteopenia associated with increased prolactin and aging in psychiatric patients treated with prolactin-elevating antipsychotics.

The aim of this study was to determine the prevalence of osteopenia in schizophrenic patients with hyperprolactinemia and to identify factors influencing bone density. Our results indicate that low bone mineral density was highly prevalent in a chronic psychiatric population treated with prolactin-elevating antipsychotics. Identified risk factors appear to be age and hyperprolactinemia for both females and males.

Adult↗

PubMed1999

Heparin-binding property of human prolactin: a novel aspect of prolactin biology.

Prolactin (PRL) shares several characteristics with growth factors and cytokines, many of which are known to bind to heparan sulfate proteoglycans. In this study we examined the heparin-binding properties of selected members of the PRL/GH family, using heparin affinity columns followed by gel electrophoresis/Western blotting. Purified human PRL and its cleaved 16K fragment, but not human GH or placental lactogen, were retained on the heparin column and were displaced by 0.5 M NaCl. Native PRL in human pituitary extracts and amniotic fluid showed a similar binding affinity to heparin as the purified hormone. None of the other hormones tested, e.g., rat, ovine and bovine PRL, glycosylated ovine PRL or rat GH, bound to heparin. Two consensus heparin-binding sequences are present in human PRL but not in the other hormones included in this study. We postulate that the heparin-binding capability of PRL affects its biological activity as a growth factor and the angiostatic actions of its 16K fragment.

Amniotic Fluid↗

PubMed2002

Gross variability in the detection of prolactin in sera containing big big prolactin (macroprolactin) by commercial immunoassays.

A high molecular mass form of prolactin (PRL), macroprolactin, accumulates in the sera of some subjects. Although macroprolactin exhibits limited bioactivity in vivo, it retains immunoreactivity. We examined the frequency of macroprolactinemia in clinical practice and the ability of immunoassay systems to distinguish between macroprolactin and monomeric PRL. Of 300 hyperprolactinemic sera identified, 71 normalized following treatment of sera with polyethylene glycol, indicating that 24% of hyperprolactinemia could be accounted for by macroprolactin. Ten of these macroprolactinemic sera were circulated to 18 clinical laboratories. Two sets of PRL measurements of the 10 untreated sera were obtained from each of the nine most commonly used immunoassay systems. Across the nine assay systems, differences in the PRL estimates ranged from 2.3- to 7.8-fold. Elecsys users reported the highest PRL levels. Somewhat lower values were reported for DELFIA systems followed by Immuno-1, AxSYM, and Architect assays. The Immulite 2000 assay generated PRL levels equivalent to approximately 50% of those reported by the high-reading methods. The lowest PRL levels were reported by Access, ACS:180, and Centaur systems. To avoid confusion caused by the frequent presence of macroprolactin accounting for hyperprolactinemia, secondary screening for the presence of macroprolactin is recommended.

Adult↗

PubMed1975

Twenty-four-hour prolactin profiles in normal and disease states: failure of thyroxine to modify prolactin secretion.

In order to assess the role of thyroid hormone on physiologically and pharmacologically induced prolactin (PRL) secretion, serum PRL concentrations were measured in 4 normal women and 4 women with various endocrinopathies before, and 4 to 6 days following, the ingestion of L-thyroxine (T4). A single 1.5 to 3.0 mg dose of oral T4 produced approximately a 2-fold increase in serum T4. Exogenous T4 did not significantly alter the mean concentration, or the pattern of PRL secretion during a 24-h interval in either normal individuals or 3 patients with galactorrhea. The lactating patients had elevated basal PRL levels and a blunted secretory response to intramuscular chlorpromazine; however, neither fasting PRL nor the peak response to chlorpromazine was altered by T4. L-Dopa suppression of serum PRL was not significantly influenced by T4 in these patients. In conclusion, PRL secretion remained unaltered after the administration of thyroxine in doses sufficient to produce approximately a 2-fold increase in serum T4. This challenges the concept that T4 and TRH are important physiologic regulators of PRL secretion.

Adult↗

PubMed1976

Prolactin and testosterone: independent circulating levels in hyperprolactinemic and normoprolactinemic amenorrhea. The effect of prolactin suppression by bromocriptine.

In order to elucidate the pituitary regulation of the female testosterone secretion, we studied by radioimmunoassay the circulating prolactin (PRL) and testosterone-dihydrotestosterone (T-dT) levels in 12 hyperprolactinemic and 12 normoprolactinemic patients with secondary amenorrhea. After the basal levels had been recorded, each patient was given bromocriptine for two weeks, 2.5 mg twice daily, and repeat estimations of the PRL and T-dT levels were done. We found no significant difference in the basal T-dT levels between normoprolactinemic and hyperprolactinemic patients, and no significant correlation between the PRL and T-dT levels in either group. Although the PRL levels of the hyperprolactinemic patients were greatly suppressed by bromocriptine, the T-dT levels showed no systematic change. In normoprolactinemic patients, the T-dT concentrations were somewhat lower during bromocriptine treatment, but the difference from basal levels was not statistically significant (0.05 less than P less than 0.1). Our results suggest that in patients with secondary amenorrhea PRL does not interfere directly with T-dT secretion, or vice versa.

Adult↗

PubMed1978

Effects of morphine on the serum prolactin levels of morphine-tolerant and nontolerant male rats and of the in vitro release of pituitary prolactin.

Morphine increased the serum prolactin (PRL) levels of male rats in a dose response manner. This effect was abolished by naloxone and apomorphine, but was not affected by diphenhydramine. The increase in the serum PRL levels by haloperidol was abolished by apomorphine, but not by naloxone. Repeated administrations of increasing doses of morphine attenuated the response of serum PRL to morphine. Naloxone did not alter the serum PRL levels of morphine-tolerant rats, while it precipitated full withdrawal signs on these rats. Although neither haloperidol nor morphine increased the release of PRL from the isolated anterior pituitary, haloperidol, but not morphine, reversed the inhibition by dopamine of the in vitro release of pituitary PRL. These results indicate that tolerance develops regarding the effect of morphine with a resulting increase in the serum PRL levels, abstinence precipitated by naloxone has no effect on the serum PRL levels, the mechanism of morphine involved in increase in the serum PRL is different from that of haloperidol as the effect of haloperidol is not antagonized by naloxone and morphine does not antagonize the effect of dopamine which inhibits the release of PRL from the anterior pituitary in vitro.

Animals↗

PubMed2000

Immunoneutralization of prolactin prevents stimulatory feedback of prolactin on hypothalamic neuroendocrine dopaminergic neurons.

We have found that exogenous prolactin (PRL) stimulates all three populations of hypothalamic neuroendocrine dopaminergic neurons. In this study, we investigated the effects of immunoneutralization of endogenous PRL on the activity of these neurons. Injection of 17beta-estradiol (E2) (20 microg subcutaneously) 10 d after ovariectomy induced a proestrus-like increase in PRL in peripheral plasma the following afternoon. At 1000 h the day after E2 injection, rats received either rabbit antirat PRL antiserum (PRL-AS) (200 microL) or normal rabbit serum (NRS, 200 microL, controls) intraperitoneally. Groups of rats were then decapitated every 2 h from 1100 h to 2100 h. Trunk blood was collected and serum extracted with protein A to remove the PRL-AS/PRL complex, and the remaining free PRL was measured by radioimmunoassay. Sites of neuroendocrine dopaminergic nerve terminals, the median eminence (ME), and intermediate and neural lobes of the pituitary gland were excised and stored for determination of dopamine (DA) and 3,4-dihydroxyphenyl acetic acid (DOPAC) concentrations by high-performance liquid chromatography electrochemical detection (EC). In addition, the anterior lobe of the pituitary gland, the locus of DA action, was collected. The concentration of PRL in NRS-treated animals increased by 1500 h, peaked by 1700 h, and returned to low levels by 2100 h. PRL-AS prevented the increase in PRL secretion in response to E2. The turnover of DA (DOPAC:DA ratio; an index of dopaminergic neuronal activity) in the ME of NRS-treated animals increased at 1500 h and rapidly returned to basal levels. Treatment with PRL-AS prevented the increase in DA turnover in the ME. DA turnover in the intermediate lobe increased coincident with the peak of PRL in serum of NRS-treated rats. PRL-AS administration prevented increased DA turnover in the intermediate lobe. The turnover of DA in the neural lobe increased by 1300 h and decreased steadily through 2100 h. However, administration of PRL-AS minimally suppressed the turnover of DA in the neural lobe. Moreover, administration of PRL-AS attenuated the rise of DA in the anterior lobe associated with the waning phase of the E2-induced PRL surge. These results clearly indicate that endogenous PRL regulates its own secretion by activating hypothalamic neuroendocrine dopaminergic neurons.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1987

[The properties of prolactin secretion in patients with prolactin secreting pituitary adenomas].

Plasma prolactin (PRL) responses to several exogenous agents are variable in patients with prolactinomas. In this study the factors determining the responsiveness to exogenous stimuli were investigated in 35 patients with prolactinomas. Among these patients, 14 patients were responder (greater than 150% increase of basal value) to TRH, sulpiride (DA D2-receptor blocker) and arginine, and remaining 21 were non-responder to these three agents. Plasma TSH responses to sulpiride, an indirect indicator of hypothalamic dopaminergic tone on pituitary gland, were similar between responder (delta TSH: M +/- SEM; 5.3 +/- 0.2 microU/ml) and non-responder (delta TSH: 5.6 +/- 0.2 microU/ml), and were greater than those in normal subjects (delta TSH: 0.7 +/- 0.2 microU/ml, n = 18) (P less than 0.001). The plasma PRL responses to dopaminergic agents (L-dopa, CB-154, dopamine) were greater in responders than in non-responders (% of basal: L-dopa, 33.7 +/- 3.7% vs 51.6 +/- 5.6% at 150 min, P less than 0.05; CB-154, 16.5 +/- 2.6% vs 30.9 +/- 2.8% at 6 hr, P less than 0.05; dopamine, 31.7 +/- 5.6% vs 44.9 +/- 4.3% at 90 min, P less than 0.05). When all patients were divided into microadenoma (n = 12) and macroadenoma patients (n = 23), there were no differences in plasma PRL responses to these agents between the two groups. Again, there were no differences in the duration of illness between the responder and non-responder patients (61.9 +/- 13.7 vs 54.1 +/- 12.0 months). During the short term CB-154 treatment (7.5mg/day for 3 approximately 5 weeks) in 8 responders and 15 non-responders, all responder patients showed normalization of plasma PRL levels, while such normalization was observed in only 6 non-responder patients. These results suggest that in prolactinoma patients variable responsiveness to several exogenous agents are depending on the sensitivity to several exogenous agents are depending on the sensitivity of prolactinoma itself, regardless of the endogenous hypothalamic dopaminergic tone, tumor size or duration of the illness.

Adenoma↗

PubMed1976

Radioimmunoassay of rat prolactin and its use in measuring prolactin production by cultured pituitary cells.

A sensitive and specific radioimmunoassay has been developed for rat prolactin (rPRL), employing the double antibody solid phase technique for the separation of free and antibody-bound [125I]rPRL. The anti-serum was raised in rabbits and showed no cross-reaction with rat growth hormone (rGH), follicle stimulating hormone (rFSH), luteinizing hormone (rLH) and thyrotrophin (rTSH). The immunosorbent (sheep anti-rabbit IgG bound to cellulose) showed a surprisingly high binding of [125I]rPRL, but not of the other iodinated anterior pituitary hormones. Addition of serum to the incubation mixtures prevented the binding between [125I]rPRL and the immunosorbent. Three different clonal strains of pituitary cells have been examined for production of rPRL, rLH and rTSH, both in the basal state as well as after treatment with thyrotrophin releasing hormone (TRH) and gonadotrophin releasing hormone (LH/FSH-RH). Monolayer cultures of two of the cell strains produced and secreted rPRL spontaneously, and they showed a 2-fold increase in rPRL production after treatment with TRH (3-10(-7) mol/1). The third cell strain did not produce rPRL spontaneously, or after treatment with TRH. None of these cell strains could be stimulated to produce rTSH by treatment with TRH. Treatment of the same three cell strains with LH/FSH-RH (1.2-10(-6) mol/1) failed to induce production of rLH, and there were no changes in production of rPRL. Prostaglandins E1 and E2 (3-10(-8) mol/1) and oestradiol-17beta (10(-7)-10(-10) mol/1), however, stimulated the production of rPRL. The effects of TRH and prostaglandins E1 and E2 were observed within 24 h of treatment, while the first effect of oestradiol-17beta was seen after 3 days. These results suggest that the stimulatory effect of oestradiol-17beta on rPRL production differs from that of TRH and prostaglandins.

Animals↗

PubMed1977

Localization of prolactin binding in prostate and testis: The role of serum prolactin concentration on the testicular LH receptor.

Specific binding sites for prolactin (PRL) and gonadotrophins on ventral and dorsolateral prostate as well as on Leydig cells and tubules of testes of rats at different ages were examined. The binding sites for PRL were found in greatest number in ventral prostate and in Leydig cells. LH binding sites were also more numerous than FSH binding sites in the latter. FSH sites were greater than LH sites in tubular preparations obtained from the testis. Specific binding (SB) of PRL in the Leydig cells reached a maximum at 45 days (4%) and in the case of LH a maximum of 12% was obtained at 70 days. In both preparations SB of FSH exhibited a plateau between 20 and 40 days (11%) followed by a gradual decline to 6% at 100 days. Following 20 dyas of treatment with Bromocriptin beginning at 20 days serum PRL was suppressed and SB of LH to the Leydig cells was significantly decreased, whereas SB of PRL and FSH was unaffected. These studies suggest that despite decreases in serum PRL, the number of PRL and FSH receptors remain unaltered. On the contrary, LH receptors in the rat testis are modulated by changes in serum PRL.

Age Factors↗