Prolactin

About: Prolactin is a research topic. Over the lifetime, 22356 publications have been published within this topic receiving 609537 citations. The topic is also known as: lactotropin, & PRL,.

Pituitary Gland Function after Disconnection from Direct Hypothalamic Influences in the Sheep

Abstract: A surgical procedure is described for isolating the pituitary gland from hypothalamic influences in sheep. The procedure results in total deafferentation of the stalk and median eminence but maintains the blood supply to the pituitary gland. The median eminence, pituitary stalk and anterior face of the pituitary gland were exposed by a transnasal, transphenoidal approach. In early studies section of the pituitary stalk as close as possible to the pituitary gland caused almost total infarction of the gland. Attempts were made to disconnect the pituitary gland from the hypothalamus by section immediately above the lateral inputs of the superior hypophyseal arteries but variable results were obtained, always with infarction of part of the pars distalis. When the pituitary gland was disconnected from the hypothalamus by entering the median eminence above the portal circulation and evacuating the nervous tissue of the tuber cinereum, (hypothalamo-pituitary disconnection; HPD), a small area of infarction was found in the pars distalis of only 1/10 cases. HPD effectively disconnected the pituitary gland from hypothalamic control whilst the pars distalis was not deprived of its blood supply. Complete severance of hypothalamo-pituitary connections also caused atrophy of the pars nervosa and enlargement of the cells of the pars intermedia. Following HPD, plasma LH and FSH concentrations diminished and plasma prolactin concentrations rose. On the day after surgery there were no LH, FSH or prolactin responses to 50 micrograms (i.m.) of oestradiol benzoate indicating the functional isolation of the pituitary gland from the hypothalamus. The isolated pituitaries were capable of responding to gonadotropin releasing hormone by LH release. Disconnection of the pituitary gland from the hypothalamus by subpial deafferentation provides a good in vivo isolated pituitary model in the sheep.

Prolactin–progesterone antagonism in self regulation of prolactin receptors in the mammary gland

Abstract: THE role of prolactin during growth of the mammary gland and in lactation is well established (see ref. 1 for review) and the antagonising action of progesterone on lactogenesis (but not on mammary growth) has been recognised2–4. A specific receptor for prolactin has been described5 and purified6 and it seems that the level of this receptor in the target cells is very sensitive to hormonal environments and might be one of the essential parameters which modulates the intensity of prolactin action. Titration of this receptor under controlled hormonal conditions has been mainly performed in the liver and its concentrations found to be sensitive to oestrogens7; this effect may be amplified or even mediated by prolactin itself8. We have shown9 that the number of prolactin receptors in the mammary gland of pregnant or lactating rabbits undergoes a sudden increase at the onset of lactation but that the Ka of the receptor–hormone interaction remains constant. The question arises as to which hormonal environment is required for this amplification; is the inhibitory action of high progesterone levels on lactogenesis associated with a reduction of receptor concentrations? We describe here a study of this possibility and of the positive regulation of prolactin on its own receptors in the rabbit mammary gland. We extend to the mammary gland the stimulating effect of prolactin on the levels of its receptors and demonstrate an antagonising action of progesterone on this process.

Induction of a lactogenic receptor in rat liver: influence of estrogen and the pituitary.

Abstract: A receptor exists in female rat liver with high specificity for lactogenic hormones. Previous work showed the receptor level increased at the time of puberty in female but not male animals. Pregnancy caused a further substantial increase. Here we show that estrone (50 μg/day) administration to male rats induced a 10- to 30-fold increase in specific binding of ovine prolactin and human growth hormone after 8-12 days with a significant increase first seen after 4 but not 2 days of injection. In females, this regimen increased binding to pregnancy levels. In prepuberal (20-days-old) male and female rats, estrone was also markedly stimulatory. The binding sites for ovine prolactin and human growth hormone were of high affinity in liver membranes from both female and estrone-treated male rats (Ka = 0.6 to 1.4 × 109 M-1). Estrone and estradiol were equally effective in inducing the lactogenic receptor. Estriol (50 μg/day), progesterone (500 μg/day), human placental lactogen (1 mg/day), and testosterone (100 μg/day) were without influence. Hypophysectomy drastically decreased the levels of lactogenic receptor in mature female rats, and estrogen treatment failed to restore receptor levels to normal. Hypophysectomized male rats were also unresponsive to estrogen. Throughout these studies the specific binding of 125I-labeled insulin remained relatively constant. This work demonstrates estrogen induction of a lactogenic receptor. The pituitary gland appears to have a critical, though presently undefined, role in the induction process.

Relationship between stress hormones and testosterone with prolonged endurance exercise.

Abstract: Previous pharmacological and pathological studies have reported negative relationships between circulating testosterone and certain stress hormones (i.e., cortisol and prolactin) in humans. These relationships have subsequently been used in hypotheses explaining the subclinical resting testosterone levels often found in some endurance-trained males, but as of yet no one has specifically examined these relationships as they relate to exercise. Thus, we examined the relationship between total and free testosterone levels and cortisol, and between total and free testosterone and prolactin following prolonged endurance exercise in trained males. Twenty-two endurance-trained males volunteered to run at 100% of their ventilatory threshold (VT) on a treadmill until volitional fatigue. Blood samples were taken at pre-exercise baseline (B0); volitional fatigue (F0); 30 min (F30), 60 min (F60), and 90 min (F90) into recovery; and at 24 h post-baseline (P24 h). At F0 [mean running time = 84.8 (3.8) min], exercise induced significant changes (P<0.05) from B0 in total testosterone, cortisol and prolactin. All three of these hormones were still significantly elevated at F30; but at F60 only cortisol and prolactin were greater than their respective B0 values. Free testosterone displayed no significant changes from B0 at F0, F30, or the F60 time point. At F90, neither cortisol nor prolactin was significantly different from their B0 values, but total and free testosterone were reduced significantly from B0. Cortisol, total testosterone and free testosterone at P24 h were significantly lower than their respective B0 levels. Negative relationships existed between peak cortisol response (at time F30) versus total testosterone (at F90, r=−0.53, P<0.05; and at P24 h, r=−0.60, P<0.01). There were no significant relationships between prolactin and total or free testosterone. In conclusion, the present findings give credence to the hypothesis suggesting a linkage between the low resting testosterone found in endurance-trained runners and stress hormones, with respect to cortisol.

Ontogeny of Prolactin Cells in Neonatal Rats: Initial Prolactin Secretors also Release Growth Hormone*

Abstract: Reverse hemolytic plaque assays and immunocytochemistry were used to monitor the ontogeny of individual hormone-secreting and hormone-containing cells in rats. Monodispersed anterior pituitary cells from fetal rats (sex unspecified) and neonatal rats of each sex were cultured for 24 h and then subjected to immunocytochemistry or plaque assays for PRL or GH. PRL secretors first appeared in appreciable numbers in cultures from 4-day-old animals, and by day 5, they accounted for 8–12% of all cells in culture. The percentage of GH secretors rose to a peak on day 5 (comprising ∼40% of all cells), when the values were slightly higher than those observed previously in adults. The percentage of cultured cells from 4- to 5-day-olds that released PRL or GH was not influenced by the sex of the donor animal and was consistent with immunocytochemical estimates. Using a sequential plaque assay that enabled the detection of both GH and PRL release from the same cells, we found that of every 100 pituitary cells from 5-da...