Effects of estrogen and testosterone on specific prolactin binding in the kidneys and adrenal of rats

Sex Differences in Renal Function: Participation of Gonadal Hormones and Prolactin

Kidney pathophysiology is influenced by gender. Evidence suggests that kidney damage is more severe in males than in females and that sexual hormones contribute to this. Elevated prolactin concentration is common in renal impairment patients and is associated with an unfavorable prognosis. However, PRL is involved in the osmoregulatory process and promotes endothelial proliferation, dilatation, and permeability in blood vessels. Several proteinases cleavage its structure, forming vasoinhibins. These fragments have antagonistic PRL effects on endothelium and might be associated with renal endothelial dysfunction, but its role in the kidneys has not been enough investigated. Therefore, the purpose of this review is to describe the influence of sexual dimorphism and gonadal hormones on kidney damage, emphasizing the role of the hormone prolactin and its cleavage products, the vasoinhibins.

Prolactin binding sites in the adrenal glands of mink (Mustela vison)

1. The purpose of this study was to determine if the mink adrenal gland might be a target organ for prolactin by establishing whether or not binding sites for the hormone exist in adrenal cell membranes. 2. Adrenal glands were collected from adult female mink in November, 1991, homogenized and subjected to differential centrifugation into three particulate fractions; 1500, 15,000 and 50,000 g. All binding determinations were made using 125I-oPRL and 200-300 micrograms protein from the 50,000 g particulate fraction. Optimal binding occurred within 8 hr at 25 degrees C. 3. Scatchard analysis of saturation data revealed a single set of high affinity (Kd = 9.27 x 10(-11) +/- 1.63 M), low capacity (Bmax = 34.22 +/- 5.37 fmol/mg) binding sites. 4. Binding sites appeared to be hormone specific as only oPRL (73% displacement) and oLH (8% displacement) inhibited binding of 125I-oPRL to adrenal membranes. No inhibition of 125I-oPRL binding to adrenal membranes occurred in the presence of a 500-fold excess of bTSH, oGH or oFSH. 5. Prolactin binding sites were readily detected in adrenal and kidney tissue, but were low in liver and almost non-detectable in spleen or lung tissue. 6. Our data suggest that the mink adrenal gland is a target organ for prolactin and that an interaction between the pituitary and adrenal glands may exist that is important for the regulation of such physiological processes as fur growth cycles.

The role of the adrenal glands in regulating onset of winter fur growth in mink (Mustela vison)

The role of the adrenal glands in regulating onset of winter fur growth in mink was investigated in long-term adrenalectomized animals. Bilateral adrenalectomy of adult female standard dark mink between June 23 and July 11, 1990, initiated onset of winter fur growth approximately 6 weeks earlier than controls. One month following completion of the winter fur growth in adrenalectomized mink, molting and growth of a new coat was observed. The type of pelage that grew as a result of the second growth wave was less dense than the normal summer or winter fur. However, this renewed hair growth suggests that adrenal hormones not only inhibit the onset of winter fur growth but also influence the duration of inactivity following each period of hair growth. Administration of deoxycorticosterone as a mineralocorticoid supplement had no effect on initiation of fur growth. It would appear that adrenal hormones are part of the mechanism through which photoperiod regulates fur growth in the mink. The identity of the adrenal hormones and their site of action is unknown.

Is prolactin playing a role in the regulation of catecholamine synthesis and release from male rat adrenal medulla?

Previous evidence allows one to suspect that prolactin (PRL) may be a physiological regulator of catecholamine (CA) synthesis and release in the adrenal gland of rodents. To explore this possibility, we studied the in vivo and in vitro metabolism and release of noradrenaline (NA) and adrenaline (A) in the adrenal gland of male rats. The study was carried out with animals exhibiting a moderate increase in plasma PRL levels induced by grafting of additional pituitaries or a severe hyperprolactinemia produced by diethylstilbestrol (DES)-induced pituitary hyperplasia. The latter animals exhibited a significant increase in adrenal weight, associated with decrease in tyrosine hydroxylase (TH) activity and in NA content. Moreover, the adrenal activity of phenylethanolamine-N-methyl transferease (PNMT) was decreased in DES-treated animals. Pituitary-grafted rats also displayed an increased adrenal weight, together with decreases in the activities of PNMT, catechol-O-methyl transferase and monoamine oxidase. These in vivo observations were followed by in vitro studies, which showed a decrease in the basal release of both CAs from incubated adrenals of DES-treated rats, with no changes in pituitary-grafted rats. In addition, exposure to PRL of the incubated adrenals of animals exhibiting normal PRL levels produced decreases in A release and storage and in TH activity. These observations allow us to conclude that: i) PRL appears to exert an inhibitory influence on the catecholaminergic activity in the adrenal gland; and ii) its effect seems to be exerted by a direct action on this gland.

Porcine adrenal prolactin receptors: characterization, changes during neonatal development and effects of hypoprolactinemia

1. Adrenal prolactin (PRL) receptors were identified within the adrenal cortex of pigs (Sus domesticus), and found to be located specifically on isolated zona fasciculata/reticularis cells (6437 sites per cell). 2. These PRL receptors were associated with binding to [125I]-oPRL which was characterized as being time and temperature dependent, specific for PRL, saturable, of high affinity (Ka = 10(10)/M) with a single class of binding sites, and irreversible except under extreme conditions. 3. The concentrations (fmol/mg protein) of PRL receptors decreased by 35% (P less than 0.05) between 3 and 10 days of age, and subsequently remained constant until 30 days of age. Total content (fmol/paired adrenals) increased progressively (2-fold, P less than 0.05) between 3 and 30 days of age. 4. Short-term (less than 16 hr) and prolonged (7 weeks) hypoprolactinemia (46-64% of control levels, P less than 0.05) were not associated with changes in numbers of porcine adrenal unoccupied PRL receptors.

Possible direct effect of prolactin on catecholamine synthesis and release in rat adrenal medulla: in vitro studies

It has been recently shown that chronic increase in circulating prolactin (PRL) levels can affect the catecholamine (CA) synthesis and release in the adrenal medulla of female and male rats. However, it is not established if this effect is directly exerted on the adrenomedullary cells. To elucidate this question, we have studied the possible capacity of PRL to modify the in vitro synthesis and release of CA in isolated adrenal medullas of female rats. The study has been performed in animals with hyperprolactinemia induced by pituitary grafts (GRAFT) or with low PRL levels induced by ovariectomy (OVX), and in their respective sham-operated controls (SHAM), in order to establish if the previous plasma levels of this hormone could modify the effects observed in vitro. Basal release of adrenaline (A), noradrenaline (NA) and total CA observed during the first h of tissue incubation was similar in the three groups of animals. However, OVX animals exhibited a decreased release of both CA in the second h of incubation. This low CA release was partially reversed after the exposure of the incubated adrenal medullas of these animals to a medium containing PRL, whereas this hormone was ineffective to modify the CA release in SHAM and GRAFT animals. Moreover, PRL caused a significant decrease in the A production by the adrenal medullas of SHAM animals, since the amount of A released plus the amount of A stored after incubation in presence of PRL was significantly decreased. Finally, the exposure of the adrenomedullary cells from GRAFT rats to PRL was followed by an increase in the contents of both NA and A in the tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone-binding proteins in high-speed cytosols of multiple tissues of the rabbit

Soluble, specific binding protein(s) for growth hormone (GH) have been identified and partially characterized in high-speed cytosolic preparations from a number of rabbit tissues. The binding of 125I-labelled human GH to proteins in liver, heart, adipose tissue, skeletal muscle and kidney cytosols was dependent on time and cytosolic protein concentration. By Scatchard analysis, the binding affinities (KA: (2-7) X 10(9) M-1) were somewhat higher than those generally reported for membrane GH receptors. The binding proteins had a greater specificity for somatotrophic hormones than lactogenic hormones, although the kidney appeared to have, in addition, a lactogen-binding protein. By gel filtration, the Mr of the cytosolic GH-binding protein was approximately 100 000 in all tissues. None of the binding proteins was detectable by the poly(ethylene glycol) precipitation method used widely for soluble hormone receptors. The cytosolic GH-binding proteins also cross-reacted with a monoclonal antibody to the rabbit liver membrane GH receptor. These results indicate the ubiquitous presence of apparently naturally soluble GH-binding proteins in the cytosolic fractions of several tissues in the rabbit. Of great interest is their presence in muscle, where GH receptors or binding proteins have not previously been detected, despite muscle being recognized as a classical GH target tissue.

The ontogeny of specific prolactin binding sites in the rat choroid plexus

The development of prolactin receptors in the choroid plexus of the rat was examined using the in vivo autoradiographic approach employing the principle of competitive binding. Experimental animals were injected with [125I]prolactin alone (total binding) while control animals received [125I]prolactin and a 500-fold excess of unlabelled prolactin (non-specific binding). Newborns as well as animals 10, 14 and 18 days postnatal were studied. Three minutes following hormone injection animals received an intracardiac perfusion with fixative and tissues were prepared for quantitative light microscopic autoradiography. The choroid plexus first demonstrated specific binding of prolactin, i.e. a statistically significant difference in the autoradiographic reactions between experimental and control animals, at 14 days postnatal. The lactogen specificity of these binding sites was further defined by the ability of [125I]prolactin to be displaced by unlabelled human growth hormone, which is lactogenic in rats, and not by unlabelled insulin, which is structurally dissimilar to prolactin. Morphometric analyses were performed on electron micrographs of choroid plexus from 10- and 14-day postnatal rats. The volume densities of constituents known to be enriched in polypeptide hormone receptors were measured and compared. Small cytoplasmic vesicles and tubules were statistically significantly more abundant in 10-day-old rats than in 14-day-old animals. It is conjectured that these vesicles and tubules contain an intracellular pool of prolactin receptors whose decrease at 14 days parallels the expression of specific binding sites at the cell surface.

Ontogeny of the sex steroid and prolactin receptors in the male rat adrenal gland

Cytosolic estrogen and androgen receptors and membrane prolactin-binding sites in the male adrenal glands showed a definite pattern during sexual development. The level of sexual steroid receptors paralleled adrenal growth, whereas prolactin binding reached its maximum value in mature rats.

Prolactin regulation of prolactin binding sites in pancreatic islets and adrenal glands of ovariectomized rats

The role of prolactin (Prl) in the regulation of Prl binding to its specific binding sites was studied in the Langerhans islets, adrenal gland and liver of adult ovariectomized female rats. Animals were sc injected twice daily during 10 days with ovine Prl (1 mg/kg BW), sulpiride (30 mg/kg BW) and bromocriptine (3 mg/kg BW). At the end of the treatment period, the animals were killed and serum was collected for Prl assay. Total Prl binding sites were measured in the membrane fraction of tissue by desaturating the occupied membrane receptors in vitro with 4M MgCl2. Serum levels of Prl were significantly higher in sulpiride-treated animals, whereas bromocriptine administration rendered undetectable values. Prolactin and sulpiride treatment significantly reduced Prl binding to the adrenal gland and Langerhans islets, whereas it greatly increased Prl binding to the liver. On the other hand, bromocriptine increased Prl binding sites in the adrenal gland and Langerhans islets, but in the liver caused no apparent effect. The binding affinity (Ka) in each tissue remained unchanged under the different experimental conditions. In addition, the binding of Prl to pancreas islets membranes was lower in late pregnancy when compared with control rats. All of these data provide strong evidence in favor of a role for Prl in regulating the number of its own tissue binding sites.

Human somatotropin binding to rabbit kidney microsomal fraction

Specific binding of 125I-labelled human somatotropin was demonstrated in microsomal membranes (microsomes) from rat and rabbit kidneys. Female rabbit kidney microsomes showed the highest binding activity and were used for further study. The association of 125I-labelled human somatotropin was time- and temperature-dependent and the binding reaction was reversible. Scatchard analysis of saturation data indicated a dissociation equilibrium constant, KD, of 56 pM and a binding capacity of 37 fmol per mg of protein. Similar results were obtained from competition experiments. Binding of 125I-labelled human somatotropin to the microsomes was specifically inhibited by hormones with lactogenic activity. The binding sites, as well as 125I-labelled human somatotropin, were not inactivated on incubation. Treatment of the microsomes with trypsin and chymotrypsin decreased the specific binding by over 90%. Preheating of the microsomes at 55 degrees C for 15 min abolished 50% of the specific binding activity.

Prolactin and the renin-aldosterone axis in human pregnancy

In view of observations suggesting an osmoregulatory role for prolactin (PRL) and the central role of the renin-aldosterone system in the regulation of pressure-volume homeostasis, this study was undertaken to determine whether acute drug-induced alterations in circulating PRL had any effect on mean arterial blood pressure (MAP), serum osmolality, and the renin-aldosterone response during early pregnancy. Bromocriptine suppressed mean baseline PRL by 83% (p > 0.05), whereas chlorpromazine increased it more than twofold (p < 0.05) during a 180-minute study period. MAP, mean serum osmolality, plasma renin activity, and aldosterone concentrations were not significantly different from mean baseline values after the administration of either drug. These data suggest that, during early pregnancy, the renin-aldosterone axis is independent of PRL and resistant to the beta-adrenergic agonist effect of chlorpromazine.

Prolactin modulation of dehydroepiandrosterone sulfate secretion

To clarify the controversy about the effect of prolactin (PRL) on dehydroepiandrosterone sulfate (DHEA-S), this study was undertaken to investigate the effects of alterations in plasma PRL on plasma DHEA-S concentrations in hyperprolactinemic women, as well as in normal male subjects. DHEA-S was measured in a group of 21 women with hyperprolactinemia, galactorrhea, and amenorrhea (PRL:257 +/- 89 ng/ml; mean +/- SEM). In these women, mean plasma concentrations of DHEA-S (2.54 +/- 0.2 microgram/ml) were significantly higher (p < 0.005) than those in 41 normal control women (1.78 z microgram/ml) and those in a group of 11 amenorrheic patients (1.77 +/- 0.2 microgram/ml). Eight women with hyperprolactinemia were given 5 mg of bromocriptine each day for 4 consecutive weeks. Within 1 week of medication, PRL levels fell by 60% (p < 0.05). To test whether lowering normal plasma levels of PRL would affect plasma concentrations of DHEA-S, five normal male subjects received a 48-hour infusion of dopamine at an average rate of 6 microgram/kg/min. Plasma levels of PRL fell by 60% (p < 0.01) after 8 hours of infusion, and DHEA-S decreased by 27% by 16 hours (p < 0.05). These data suggest that PRL modulates the secretion of DHEA-S: an increase in plasma levels of PRL is correlated with elevated concentrations of DHEA-S, whereas a decrease in PRL is followed by a fall in DHEA-S.

Plasma prolactin, human chorionic gonadotropin, estradiol, testosterone, and progesterone in the ovarian hyperstimulation syndrome

Plasma prolactin, estradiol, progesterone, and testosterone, but not HCG-beta levels, were higher in a patient who developed the ovarian hyperstimulation syndrome while undergoing ovulation induction with human gonadotropins than in two other women who also became pregnant after similar treatment without complications. These results suggest that hyperprolactinema, in association with elevated ovarian steroid levels, may be factors in the pathogenesis of this disorder.