Regional mechanisms within anterior pituitary of lactating rats may regulate prolactin secretion

Prolactin (PRL) release was compared after incubating the central and peripheral regions of the anterior pituitary of lactating rats, either nonsuckled or suckled in conditioned medium obtained by incubating medium with the same anterior pituitary regions from nonsuckled or suckled rats. To collect conditioned media, anterior pituitary regions were incubated in Earle’s medium for 4 h, and conditioned medium was filtered and employed double concentrated. Each anterior pituitary was incubated in conditioned medium for 30 min. PRL released in vitro was determined by polyacrylamide gel electrophoresis. As a control, anterior pituitary regions from lactators were incubated in medium conditioned by male rat anterior pituitary regions, and they showed no changes of PRL release compared with those cultured in Earle’s medium. In general, conditioned media from both anterior pituitary regions of nonsuckled and suckled rats inhibited PRL release in peripheral anterior pituitary regions, whereas PRL release was stimulated in central regions of both nonsuckled and suckled rats. A higher number of stimulatory effects was provoked by conditioned media from suckled than from nonsuckled rats, and most of these effects were from conditioned media of the peripheral region of suckled rats. Together, these results suggest the existence within anterior pituitary regions of factors that regulate PRL secretion and that their action depends on the physiologic condition of the animal.     

Hysterectomy-induced alterations in prolactin secretion of lactating rats

The contribution of the uterus to the regulation of PRL secretion in lactating dams and cycling female rats was investigated. Lactating animals were hysterectomized or sham operated 2 days after parturition, and the number of pups was adjusted to eight. Blood samples for PRL RIA were obtained through intra-atrial cannulae implanted 2 days before experimentation. In order to study the PRL secretory profile in undisturbed freely lactating rats, blood samples were taken every 2 h for 24 h starting at 1400 h. During early lactation (days 7-8), hysterectomy did not alter the PRL secretory profile compared to that of sham-operated controls. On days 14-15 post partum, PRL secretion followed a characteristic bimodal pattern showing two PRL surges at 1800 h and 0600 h. After hysterectomy, the early morning PRL surge disappeared and PRL secretion showed an unimodal daily rhythm reaching its peak at 1800 h. The possible effect of the absence of the uterus on suckling-induced PRL release at various stages of lactation was studied. On days 7-8, suckling stimuli after 4 h of pup deprivation induced robust PRL release. Hysterectomy did not significantly alter PRL release at this earlier stage of lactation. In control groups, the suckling-induced PRL secretory response markedly declined as the postpartum period advanced. On the other hand, the hysterectomized animals retained significantly greater responsiveness to suckling during the second half of lactation. These data indicate an inhibitory influence of the uterus on PRL secretion. The onset of this uterine effect is considerably delayed, and its influence became prominent only at a later phase of lactation. The effect of length of pup deprivation preceding the suckling stimulus, in combination with hysterectomy, was also investigated. Hysterectomy significantly increased suckling-induced PRL release after 4 and 24 h separation compared to the sham-hysterectomized animals. When the separation was longer than 48 h, the inducibility of PRL release by suckling declined and was not influenced by hysterectomy. In order to study the possible influence of the uterus on PRL secretion during the estrous cycle, regularly cycling female rats were hysterectomized at diestrus 1. Twelve days later the animals were cannulated, and serial blood samples were taken during the subsequent proestrus. Hysterectomy did not alter the PRL surge which occurred on the afternoon of proestrus indicating that the uterus does not have a major function in regulating PRL secretion on proestrus. In conclusion, hysterectomy significantly delayed the extinction of suckling-induced PRL release revealing the active role of the uterus in the regulation of this neuroendocrine reflex.     

Stimulation of anterior pituitary galanin and prolactin gene expression in suckling rats

Recent evidence suggests that galanin, may regulate prolactin (PRL) secretion during lactation. In this article, we describe the regulation of anterior pituitary galanin and PRL gene expression during pregnancy and after parturition in the rat. Expression of galanin and PRL in the anterior pituitary were significantly higher at d 20 of pregnancy compared to diestrus. One day after parturition, galanin mRNA levels increased a further 4.5-fold. This post partum increase in gene expression was not observed for PRL. The increase in galanin gene expression was maintained above the diestrous level for at least 10 d after parturition. PRL mRNA expression, on the other hand, was largely unchanged after parturition. Although the increase in galanin gene expression 1 d after parturition was independent of suckling, subsequently, galanin, gene expression was significantly higher in nursing mothers. Anterior pituitary galanin gene expression was 12-fold higher in nursing mothers compared with those that were not, 3 d after parturition. Similarly, PRL gene expression was significantly lower in mothers who were not suckling their pups 3 d after parturition. Initiation of suckling alone was insufficient to stimulate galanin and PRL expression. Despite suckling for 2 d, removal of the suckling stimulus subsequently resulted in a rapid decrease in galanin gene expression. Hence, the stimulatory effect of suckling on galanin expression requires a sustained suckling stimulus. In conclusion, the data support the hypothesis that anterior pituitary galanin plays an important role during lactation, likely acting to amplify lactotroph stimulation through paracrine and autocrine mechanisms.     

Mammary gland prolactin receptor and pituitary prolactin secretion in lactating mice with different lactational performance

SHN female mice, a high mammary tumour strain, are superior to SLN, a low mammary tumour strain, in lactational performance. Mammary gland prolactin receptor and pituitary prolactin secretion during lactation were compared between these strains. The binding activity, the number of receptor sites per mg tissue and the association constant were measured by the in vitro incubation of mammary gland slices with 125I-labelled bovine prolactin, and the pituitary and plasma levels of prolactin were assayed by homologous radioimmunoassay. There was only a slight difference between strains in any of the parameters for prolactin receptor and for prolactin secretion on either day 4 or day 9 of the first lactation. Almost all the correlation coefficients between each parameter for prolactin receptor and the pituitary or plasma level of prolactin were not statistically significant. These findings suggest that any parameter for prolactin examined in this study is not always directly indicative of lactational performance and further show that the individual variation in the pituitary prolactin secretion during lactation is not so great as to alter the prolactin receptor.     

Inhibition of in vivo pituitary release of luteinizing hormone in lactating rats by exogenous prolactin.

The mechanism whereby the reciprocal relationship between the plasma levels of prolactin and HL is maintained in lactating rats under different degrees of suckling stimulus has been investigated in the present study. Plasma levels of luteinizing hormone (LH) in lactating rats suckling two pups could be reduced significantly by injecting prolactin (PRL). This reduction was also evident in ovariectomized and ovariectomized-adrenalectomized lactating rats, thus excluding mediation of the inhibitory effect by steroids from end-organs. The in vivo response of the pituitary to exogenous LHRH was lower in rats suckling eight pups than those suckling two pups. Prolactin administered prior to LHRH caused an inhibition of the response of the pituitary to exogenous LHRH in rats suckling two pups. These data provide evidence for the hypothesis that in the lactating rat, in the presence of minimal suckling stimulus, the causative factor for reducing serum LH levels is prolactin, which acts by altering the pituitary responsiveness to LHRH.     

Chronic posterior pituitary lobectomy: prolonged elevation of plasma prolactin and interruption of cyclicity

We previously reported that the posterior pituitary dopaminergic system participates in the inhibition of prolactin (PRL) secretion in both male and lactating female rats. However, posterior pituitary lobectomy (Lobex) of urethane-anesthetized cycling rats resulted in an elevation in plasma PRL for a short time only. This raises a question regarding the importance of input from the posterior pituitary to the control of PRL secretion during the estrous cycle. The objectives of this study were to examine the chronic effects of Lobex on plasma PRL levels in conscious rats and to determine whether the absence of input from the posterior pituitary interferes with estrous cyclicity. Lobex or sham lobectomy were performed under Brevital anesthesia in estrous rats. Blood was collected from jugular cannula at hourly intervals on the day of surgery and at 09.00, 13.00, and 17.00 h during the following 4 days. Daily water consumption and vaginal cyclicity were monitored for 14 and 20 days, respectively. Within 2 h after Lobex, the plasma PRL levels rose 3- to 4-fold and remained elevated for 3 days before declining to near control levels on the 4th day. None of the Lobex rats resumed cyclicity within 3-4 days, 50% had an interruption of cyclicity for 4-10 days, and the remainder were noncyclic for more than 11 days. Upon resumption of cyclicity, Lobex rats had 11.3 +/- 0.4 oviductal ova which is within the normal range for intact ovulating rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

全腔镜肺叶切除与开胸肺叶切除治疗早期肺癌1年随访

目的探讨全腔镜肺叶切除与开胸肺叶切除治疗对早期肺癌患者肺功能、并发症、生活质量等的影响。方法146例早期肺癌患者根据患者意愿,以手术方式不同,分成两组,其中67例实施传统开胸肺叶切除术(开胸组),另外79例实施全腔镜肺叶切除术(全腔镜组)。对两组术中和术后恢复情况、肺功能指标、生活质量、术后并发症、术后1年预后情况进行对比。结果全腔镜组手术时间明显长于开胸组(P<0.05),但术中失血量、术后引流量要明显少于开胸组(P<0.05),切口长度、术后住院时间均明显短于开胸组(P<0.05),术后伤口疼痛程度显著低于开胸组(P<0.05),淋巴结清除个数组间无统计学差异(P>0.05)。术后1 w,两组肺功能1秒用力呼气容积(FEV1)和每分钟最大通气量(MVV)明显下降,但全腔镜组显著优于开胸组(P<0.05);在术后1年,两组肺功能已基本达到术前水平,且组间水平无统计学差异(P>0.05)。术后3个月,两组肺癌症状量表(LCSS)得分和肺癌患者生存质量测定量表(FACT-L)均较术前显著降低(P<0.05),全腔镜组LCSS得分较开胸组明显降低(P<0.05),FACT-L得分较开胸组显著升高(P<0.05);术后1年,LCSS得分的组间差异无统计学意义(P>0.05),两组FACT-L得分均达到术前水平,组间差异无统计学意义(P>0.05)。全腔镜组并发症发生率明显低于开胸组(P<0.05)。术后1年,组间在复发、远处转移和生存率差异均无统计学意义(P>0.05)。结论全腔镜肺叶切除与开胸肺叶切除治疗早期肺癌均可达到满意效果,在远期预后上效果相当,且全腔镜方案术中创伤小、术后恢复快、并发症低。     

The effect of neurotensin on pituitary secretion of thyrotrophin and prolactin in vitro

The effects of neurotensin on thyrotrophin (TSH) and prolactin (Prl) release were studied in two in vitro systems - anterior pituitary cells in culture and perifused anterior pituitary fragments. Neurotensin significantly reduced basal secretion of both TSH and Prl (P less than 0.001) from cultured pituitary cells, and abolished thyrotrophin releasing hormone (TRH)-stimulated TSH thyrotrophin releasing hormone (TRH)-stimulated TSH TSH and Prl release (P less than 0.02) from perifused pituitary fragments. These data indicate that neurotensin has a direct inhibitory effect on TSH and Prl secretion by the anterior pituitary.     

Calcitonin inhibition of prolactin secretion in lactating rats: mechanism of action

The effects of intracerebroventricular (10 ng/rat) or intravenous (10 or 40 microg/15 min/rat) administration of salmon calcitonin (sCT) on the prolactin (PRL) response to suckling and the activity of tyrosine hydroxylase (TH) were examined in lactating rats. Plasma concentration of PRL increased dramatically in control rats after the onset of the suckling stimulus, while administration of sCT resulted in inhibition of PRL response to suckling. The action of sCT was much more effective with intracerebroventricular administration, which totally blocked PRL release, compared to intravenous administration. The intracerebroventricular administration of sCT increased TH activity of tuberoinfundibular dopamine neuron (TIDA) in the stalk-median eminence, as measured by DOPA accumulation, while completely suppressing the PRL response to suckling. Injection of alpha-methyl-p-tyrosine (alpha-MT; 50 mg/kg), an inhibitor of TH and thus dopamine synthesis, increased PRL levels, and suckling caused a further increase in plasma concentrations of PRL. Injection of sCT (intracerebroventricularly) did not inhibit the PRL response to suckling in the presence of a depletion of dopamine. These results suggest that sCT inhibition of PRL secretion in lactating rats is mediated mainly by TIDA neurons without involvement of other neuroendocrine mechanisms.     

Modulation of pituitary gonadotropins and prolactin secretion by testosterone in vitro.

Investigations were undertaken to study the differential modulation of LH, FSH and PRL secretion by testosterone (T) using whole pituitary (PI) or pituitary-hypothalamus coincubates (PHC) as in vitro constructs. PI and PHC from intact and castrated rats were incubated with or without T thrice, for 24 h each, (24 h x 3, total incubation period 72 h). The spent media was replenished every 24 h. At the end of 72 h, a few of the pituitary glands were challenged with 10 nM LHRH for 4 h. The spent media and pituitary glands were analyzed for LH, FSH and PRL using specific RIAs. Incubation of PI or PHC from intact rats with T stimulated the release of LH and FSH but inhibited the release of PRL. T had no effect on the intrapituitary contents of LH but inhibited intrapituitary contents of FSH and PRL, as compared to controls incubated without T. Castration increased intrapituitary contents of LH and FSH with concomitant decrease in PRL levels. Incubation of PI or PHC from castrated rats with T inhibited intrapituitary contents of LH to intact pituitary levels, while PRL levels were further reduced instead of being ameliorated. It is concluded that PI or PHC can be used as convenient in vitro models to monitor the effect of castration or of T modulation of pituitary and hypothalamus functions. T does not affect the synthesis of LH at the gonadotroph level but facilitates the regulation of intracellular LH and FSH levels. It is postulated that T inhibits the synthesis of FSH/PRL at the gonadotroph/lactotroph levels.     

Antagonist of pituitary adenylate cyclase activating polypeptide suppresses prolactin secretion without changing the activity of dopamine neurons in lactating rats

Pituitary adenylate cyclase activating polypeptide (PACAP) is a relatively new neuropeptide, and it has a potent stimulatory effect on adenylate cyclase activity in rat pituitary cells. However, the role of PACAP in the physiological control of prolactin (PRL) secretion is still unclear. In the present study, we investigated the physiological significance of endogenous PACAP on PRL secretion in lactating rats. On lactation days 7-8, pups were separated from their mother rats for 5 h before the onset of suckling and PACAP6-38 (16 microg), a receptor antagonist, was injected through the lateral ventricle cannula just after the removal of pups. The effects of PACAP6-38 on PRL and oxytocin secretion, and on the activity of tyrosine hydroxylase (TH), were examined after the onset of suckling. Administration of PACAP6-38 inhibited PRL levels in response to suckling, but it did not affect the activity of TH, as measured by DOPA accumulation at 15 min after administration of NSD 1015 (25.0 mg/kg), an L-aromatic amino acid decarboxylase inhibitor, or the plasma concentrations of oxytocin in lactating rats. Injection of alpha-methyl-p-tyrosine (alpha-MT; 50 mg/kg), an inhibitor of dopamine synthesis, increased PRL levels, and suckling caused a further increase in the plasma concentrations of PRL. An injection of PACAP6-38 (i.c.v.) also inhibited the PRL response to suckling under dopamine depletion. These results suggest that endogenous PACAP acts as a neurotransmitter or neuromodulator within the hypothalamus and plays an important role for PRL secretion in lactating rats. Endogenous PACAP may regulate PRL secretion, possibly mediated by PRL-releasing factors such as vasoactive intestinal polypeptide or vasopressin.     

Stimulation by leumorphin of prolactin secretion from the pituitary in rats

The effect of leumorphin (LM), one of big leu-enkephalins derived from preproenkephalin B, on PRL secretion was studied in the rat in vivo and in vitro. Intracerebroventricular injection of synthetic porcine LM (0.06-6 nmol/rat) caused a dose-related increase in plasma PRL levels in urethane-anesthetized male rats and in conscious freely moving rats. Intravenous injection of LM (3 nmol/100 g BW) also raised plasma PRL levels in these animals. The plasma PRL response to intracerebroventricular LM (0.6 nmol/rat) was blunted by naloxone (125 micrograms/100 g BW, iv). The stimulating effect of LM on PRL release was the most potent among the peptides derived from preproenkephalin B. In in vitro studies, PRL release from superfused anterior pituitary cells was stimulated in a dose-related manner by LM (10(-9)-10(-6) M), and the effect was blunted by naloxone (10(-5) M). These results suggest that LM has a potent stimulating effect on PRL secretion from the pituitary in the rat by acting, at least in part, directly at the pituitary through an opiate receptor.     

Effect of thyrotropin-releasing hormone and dopamine on the in vitro secretion of prolactin by the bullfrog pituitary gland

Pituitary glands of bullfrogs (Rana catesbeiana) were incubated in medium containing thyrotropin-releasing hormone (TRH) and/or dopamine in order to see their effects on the release and synthesis of prolactin, which was measured by a homologous radioimmunoassay. Prolactin synthesis was measured by monitoring the incorporation of [3H]leucine into prolactin. TRH (0.1-10 ng/ml) stimulated the release of immunoassayable prolactin and newly synthesized [3H]prolactin into the medium in a dose-dependent manner; however, it was ineffective in increasing total prolactin (medium plus pituitary) and the incorporation of [3H]leucine into the total prolactin during the experimental period (20 hr). The TRH-induced elevation of prolactin release was suppressed by the addition of dopamine (5 X 10(-7) M) to the medium.     

Prolactin-releasing Peptide (PrRP) increases prolactin responses to TRH in vitro and in vivo

The Prolactin-releasing Peptide (PrRP) is a 31-aminoacid peptide produced and secreted from the hypothalamus, and postulated to promote the prolactin release from the pituitary. However, the action of PrRP remain controversial, since it was described to have potency comparable enough to TRH, although there are many evidences that PrRP is less potent than TRH. Here we have studied the effects of PrRP alone or in combination with TRH in the prolactin levels of rat pituitary primary cell cultures in vitro and also in vivo prolactin responses in randomly cycling and estrogens-treated female rats. PrRP itself increased prolactin levels in vitro and in vivo, although in a magnitude several times lower than TRH. In vivo PrRP promotes an atypical non-peaking progressive and maintained prolactin increase. On the other hand, PrRP markedly increased the prolactin responses to TRH in vitro (10–30 fold increase) and in vivo (up to three-fold increase). In addition, FGF-2 and EGF, two important growth factors present in the pituitary, reduced the PrRP-induced prolactin increase in vitro. Taken together our results suggest that PrRP released from the hypothalamus may be relevant to modulate the circulating prolactin levels in the rat.     

Effect of amantadine on prolactin secretion, pituitary DNA synthesis and 3H-spiperone binding in male estrogen-treated rats

Amantadine, a well-known antiviral agent, causing an increase in dopamine synthesis, release and the inhibition of re-uptake of noradrenaline and dopamine in central and peripheral catecholaminergic neurons, is successfully used in the treatment of Parkinson's disease. In the present paper, we have studied the effect of various doses of amantadine on in vivo prolactin secretion and the incorporation of 3H-thymidine and 3H-spiperone binding by the anterior pituitary gland of long-term diethylstilboestrol-treated male Wistar rats. Four weeks after a subcutaneous implantation of Silastic tubes containing 10 mg of diethylstilboestrol, a dramatic rise in serum prolactin levels was observed, accompanied by an increased uptake of 3H-thymidine by DNA anterior pituitary cells. Amantadine, given in the subcutaneous doses of 50, 5 and 0.5 mg/kg of body weight attenuated the stimulatory effect of stilboestrol on serum prolactin concentration in a dose-dependent fashion. On the other hand, the incorporation of 3H-thymidine into DNA pituitary cells in all the groups of amantadine-treated rats was only slightly suppressed. In an additional experiment, Scatchard analyses were performed on the in vitro 3H-spiperone binding kinetics in a dispersed anterior pituitary cell culture prepared from the pituitaries of 6-week diethylstilboestrol-treated rats. It has been found that amantadine injected in the dose of 5 mg/kg of body weight for 14 days induced a twofold decrease in the density of dopamine D2 binding sites (36.6 +/- 9.4 vs. 70.3 +/- 3.4 fmol/10(6) cells; p less than 0.02), while the apparent affinity of the receptors was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)