Patterns Of Prolactin Secretion Research Articles

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.

Twenty-four-Hour Secretory Patterns of Gonadotropins and Prolactin in a Case of Chiari-Frommel Syndrome

Plasma LH, FSH and prolactin secretory patterns were derived from the measurement of 20-min interval plasma samples obtained during a complete 24-h period in a patient with persistent postpartum amenorrhea and galactorrhea (Chiari-Frommel syndrome), before and after clomiphene citrate therapy. During nocturnal sleep, polygraphic monitoring was carried out to precisely identify sleep onset, specific sleep stages and waking periods. During the evening and nighttime hours, LH and FSH concentrations were markedly reduced, compared to the daytime patterns both before and after clomiphene therapy. A sleep associated rise of prolactin concentration was present, similar to the pattern found in normal subjects but at higher concentrations. The reciprocal nature of the nocturnal secretory patterns for LH and FSH and prolactin in this patient suggests an alteration in hypothalamic dopaminergic mechanisms which are thougt to control the secretion of these hormones.

The control of progesterone secretion during the estrous cycle and early pseudopregnancy in the rat: prolactin, gonadotropin and steroid levels associated with rescue of the corpus luteum of pseudopregnancy.

The hormonal factors associated with converting a corpus luteum of estrous cycle into a corpus luteum of pseudopregnancy were studied by measuring LH and FSH prolactin, estradiol and progesterone levels in decapitated rats during the 4-day estrous cycle and a comparable time of pseudopregnancy (lights on 0600-0800 hr.). During the estrous cycle, prolactin, LH and FSH remained low and unchanging except on the afternoon of proestrus, when typical proestrous surges were observed. In contrast, estradiol levels began to increase on D-1, from baseline values of 7 pg/ml to approximately 15-20 pg/ml. These levels were maintained until the afternoon of D-2 when estradiol further increased to reach peak levels of 40-50 pg/ml by 0900 hr on proestrus. Estradiol then declined in relation to the increase in LH secreation and had returned to baseline by estrus. Progesterone secretion by the corpora lutea of the cycle also increased on the afternoon of D-1 and reached a maximum value of 25-30 ng/ml early on the morning of D-2. At this time, a precipitious fall in progesterone occurred, returning to baseline values of 5-1- ng/ml by 0700 on D-2 signifying the regression of the corpora lutea of the cycle. Progesterone remained low thereafter until the afternoon of proestrus when levels increased in response to the proestrus when levels increased in response to the proestrous surge of LH. Following cervical stimulation at 1900 hr on proestrus, no differences were noted, with respect to the estrous cycle, in LH, FSH or estradiol secreation through the afternoon of D-2. Surprisingly, progesterone levels did not differ in the cycle and pseudopregnancy until the early morning of D-29 instead of progesterone levels falling to baseline as they had during the cycle, the corpora lutea of pseudopregnancy were rescused, progesterone increasing dramatically to reach levels of 45-50 ng/ml by 1700 hr on that same day. The only difference in hormone secretion that was noted which could account for this marked divergence in progesterone secretion was the pattern of prolactin secretion following cervical stimulation. In contrast to the low levels seen during the estrous cycle, biphasio surges of prolactin secretion occured each day, one being nocturnal (0100-0900 hr) and the other diurnal (1500-2100 hr). The rescue of the corpus luteum occured in association with the nocturnal surge on D-2. These results suggest that nocturnal surge on D-2, PROLACTIN IS THE MAJOR Luteotropic stimulus which transforms and estrous cycle into pseudopregnancy by prolonging progesterone secretion from the corpus luteum. Moreover, if LH is important for progesterone secretion, no changes were observed in the pattern of LH secretion which can account for the rescue of the corpus luteum.

Hypothalamic-pituitary function in diverse hyperprolactinemic states.

Prolactin secretion in normal adults is characterized by periods of episodic secretion which increase in magnitude during sleep. In this study, we report the 24-h mean prolactin concentrations, prolactin secretory patterns, and associated pituitary hormone function in nine patients (seven women and two men) with hyperprolactinemia of diverse etiologies. Four of the women and one of the men had clinically demonstrable pituitary tumors, one boy had a hypothalamic tumor, and the three other women had "functional" hyperprolactinemia. The 24-h mean prolactin concentrations derived from averaging the 20-min interval samples for 24 h ranged from 28.6 to 1,220 ng/ml. The plasma prolactin patterns in these patients showed persistence of episodic secretion in all and loss of the normal sleep-wake difference in plasma prolactin in seven of nine. Three of the patients with galactorrhea and comparable 24-h mean prolactin concentrations (58.3, 59.7, and 64.3 ng/ml) showed similar prolactin secretory patterns despite different etiologic mechanisms. Evaluation of the secretory patterns of luteinizing hormone (LH) in these patients showed loss of normal pulsatile LH release and a low 24-h mean LH concentration in the patient with the pituitary tumor, while the two patients without clinically demonstrable pituitary tumors ("post-pill" galactorrhea and "idiopathic" galactorrhea) showed normal LH secretory patterns and 24-h mean LH concentrations. The 24-h mean cortisol concentrations and secretory patterns were normal in five of the seven patients who had these parameters measured. The patient with the hypothalamic tumor had a low 24-h mean cortisol concentration and production rate and absent response to metyrapone. The patient with "idiopathic" galactorrhea had an elevated 24-h mean cortisol concentration but normal cortisol production rate and urinary 17-hydroxycorticoid excretion. Growth hormone secretion was abnormal in four of the patients (one with the hypothalamic tumor and three with pituitary tumors). Thyrotropin-releasing hormone (TRH) administration in four patients resulted in normal TSH release in two patients (one of whom developed galactorrhea after the test), an absent response in the patient with the hypothalamic tumor, and a blunted response in one of the women with a pituitary tumor. The two men had low 24-h mean plasma testosterone concentrations (69 and 30 ng/100 ml) and symptoms of impotence and loss of libido. Five of the women (four with pituitary tumors and one with Chiari-Frommel syndrome) had either low 24-h mean LH concentrations, abnormal LH secretory patterns, or both. These data indicate that patients with hyperprolactinemia encompassing a varied etiological range frequently show loss of the normal sleep-associated increase in prolactin secretion as well as abnormalities in the regulation of the other hypothalamic pituitary-regulated hormones. The finding that the abnormalities in LH, growth hormone, thyrotropin, and cortisol (adrenocorticotrophic) secretion were almost uniformly confined to the patients with the clinically demonstrable hypothalamic or pituitary tumors suggests that the size of the lesion is the critical factor.

Influence of sexual hormones on the differentiation of neural centers.

The influence of hormones on the differentiation of various neural functions is reviewed. Whether a cyclic feminine or an acyclic masculine pattern of gonadotropin secretion throughout reproductive life is established depends on the presence or absence of androgenic hormones during the appropriate period of fetal development. Androgen influence, either natural in the male sex or experimental in females, leads invariably to permanent destruction of cyclicity. The absence of androgen during a well-defined phase of fetal development allows the cyclic feminine pattern of gonadotropin secretion to continue throughout life, regardless of the genetic sex. This has been revealed through a variety of experimental approaches including castration and gonad transplantation, and androgen and antiandrogen treatment during the phase of brain differentiation. This critical period occurs before birth in most species but after birth in some others, e.g., rats and mice. Similar experiments have revealed that the pattern of prolactin secretion is also determined by early hormonal influence on neural structures. In males or experimentally androgenized females, there is less estrogenic inhibition of a hypothalamic prolactin inhibiting factor (PIF) which exerts a chronic inhibition of prolactin secretion from the pituitary. These animals respond with less prolactin release than normal females to estrogen treatment. Behavioral traits of the adult animal are also predetermined by hormonal influence during neural differentiation. If the developing brain is deprived of androgens during a critical period, the adult animal's sexual behavior will be feminine. Pertinent experiments on genetic males who were castrated or treated with an antiandrogen are described. Experimental evidence exists indicating that the higher aggressiveness of males is also predisposed by early androgen influence on the brain. The conclusion is drawn that the feminine differentiation of the brain does not require any hormonal impulses but that androgens are essential for the impression of masculinity.

The pattern of prolactin secretion during pseudopregnancy in the rat: a daily nocturnal surge.

The patterns of prolactin secretion during the estrous cycle and pseudopregnancy were determined in rats bearing chronic aortic catheters from which blood samples were withdrawn at 2-hr intervals throughout both reproductive states. Prolactin concentrations were determined by radioimmunoassay. Except for the spontaneous proestrus surges observed at the beginning and end of the blood collection, plasma prolactin concentrations during the estrous cycle were low, never rising above 10 ng/ml. In pseudopregnant animals, prolactin concentrations were highly erratic but significantly elevated during the 24 hr period following cervical stimulation. Beginning on day 1 and at approximately 24-hr intervals thereafter through day 11, a surge of prolactin secretion occurred, beginning at 0100 hr, peaking at 0300–0500 hr and terminating by 0900–1100 hr. Maximal mean prolactin values during the surges ranged from 40–110 ng/ml. These daily nocturnal surges of pseudopregnancy alternate daily with a period from 1100 hr to ...

Effects of electrochemical stimulation of the hypothalamus on serum prolactin and LH in rats.

Plasma levels of prolactin and LH were measured by radioimmunoassay following electrochemical stimulation of the medial preoptic area (MPO) or the arcuate nucleus (Arc.N.) in pentobarbital anesthetized proestrous rats. Differences in the secretion pattern of prolactin and LH were observed when stimulated by means of acutely or chronically implanted electrodes. Acute implantation and stimulation of the MPO resulted in no change in serum prolactin levels, whereas stimulation by means of chronically implanted electrodes evoked a marked increase in serum prolactin. The general observation was that electrostimulation in the acute experiments causes a less sharp but more prolonged prolactin and LH release from pituitary than stimulation through chronically implanted electrodes.

Studies on Maintaining the Lactational Diestrum after Early Litter Weaning

The litters of lactating rats were adjusted to 8 pups on the day of parturition (day 1 of lactation) and various methods of cervical stimuli were performed. The litters were weaned at regular intervals and vaginal smears were examined for the return of estrous cycles. Thirty percent of mothers who either were not suckled or were suckled for 48 hr showed diestrus smears for 10 days or more. Mothers whose litters were removed on days 6, 9, and 12 of lactation did not exhibit an extended diestrum. Mechanical stimulation of the cervix of mothers weaned on day 3 of lactation did not increase the incidence of extended diestrus from the controls; electrical stimulation, however, almost doubled the number responding (50 vs. 30%). If the initiation of vaginal smearing was delayed from the first day of lactation until the third, none of the animals had pseudopregnancy-like vaginal smears. Estradiol administration on day 1 of lactation resulted in 60% of the animals exhibiting an extended diestrum. Combining both estradiol injection and mechanical cervical stimulation resulted in a slightly lower percentage (40%). The suckling stimulus is believed to induce an acute pattern of prolactin secretion while cervical stimulation induces a chronic pattern. The summation of these two secretory patterns may be observed early in lactation.