Richard R. Gala

Prolactin and growth hormone in the regulation of the immune system

Abstract Evidence implicating prolactin (PRL) and growth hormone (GH) in the regulation of the immune system has been reviewed. Hypophysectomized animals have deficiencies in both cell-mediated and humoral immunological functions and either PRL or GH corrects these deficiencies. Animals administered bromocryptine, a drug that specifically blocks PRL release, have impaired immune responses similar to hypophysectomized animals, and again both PRL and GH correct these deficiencies. Genetically dwarf animals, which lack both PRL and GH, are also immunocompromised, and once again PRL and GH can correct the deficiencies. In dwarf animals, however, fewer studies have examined PRL actions. In growth-deficient children, immune function is not dramatically altered and basal secretion of GH has been reported. Very few clinical studies have examined whether PRL secretion is also deficient, and this may explain why a clear loss in immune function is not evident in growth-deficient children. In a number of species, including man, both PRL and GH stimulate thymic function and increase the secretion of thymulin, a thymic hormone. No studies, however, have reported on the effects of PRL and GH on other thymic hormones. A number of studies have reported in vitro effects of PRL and GH on cells involved with immunity, and the presence of high-affinity PRL and GH receptors have been observed on a number of these cells. The action of GH on the proliferative response of cells involved with immunity in vitro appears to be mediated by the production of insulin-like growth factor I. The effect of PRL on insulinlike growth factor I production by these ceils has not been examined. One of the most consistent findings from in vitro studies is that prolactin antisera blocked a number of immune reactions. This led to the discovery that cells involved with immunity appear capable of producing PRL and GH, but the physiological significance of these observations have not been explored. There is a great need to identify the cell types responding to PRL and GH and this should be a goal of future investigations. There is also a need for investigators to be aware that both PRL and GH are involved in the regulation of the immune system and to design experiments to elucidate where each functions in the maturation cascade of cells involved with immunity. From the evidence available, it is apparent that PRL and GH have an important function in the immune system and future investigations should be directed toward elucidating their site(s) of action.

The physiology and mechanisms of the stress-induced changes in prolactin secretion in the rat

It is well known that stress in a number of forms induces the secretion of prolactin (PRL) in a number of species. What is not well known is that under certain conditions stress will also induce a decrease in PRL secretion. The conditions whereby stress decreases PRL are those where PRL secretion is elevated such as during the proestrous afternoon surge and during the nocturnal surge of pseudopregnancy. The physiologic significance of the stress-induced increase of PRL is suggested to be important in maintaining the competence of the immune system. The significance of the stress-induced decrease of PRL does not appear to have a major consequence on the physiology of reproduction in the rat and it is suggested that future studies be directed towards its significance in the immune system. The literature is reviewed dealing with the regulation of PRL secretion with emphasis on the factors that generate PRL surges in the rat. In addition the mechanism(s) of the stress-induced increase and decrease is (are) also examined. A hypothesis is presented suggesting an interaction between tuberoinfundibular dopamine secretion and a hypothalamic prolactin releasing factor in the generation of PRL surges and the differential effects of stress on PRL secretion.

Rat lymphoma cell bioassay for prolactin: observations on its use and comparison with radioimmunoassay

The rat Nb2 node lymphoma cell bioassay (BA) for prolactin (PRL) was validated for use in our laboratories. During the course of this validation we observed that rat prolactin (NIAMDD-RP-1) stimulated cell division by as much as 16.5 fold over the range of 0.04 to 40.0 ng/ml at the end of 72 hours of incubation. We also observed a dose related increase in the size of the lymphoma cells. Prolactin concentrations in rat plasma, serum, anterior pituitary (AP) homogenates and milk were measured by both radioimmunoassay (RIA) and BA. In individual BAs there was parallelism between samples and standard; but when several dilutions of the same plasma and pituitary homogenates were assayed repeatedly, higher PRL levels were consistently observed for the more concentrated samples. At low or moderate levels of plasma PRL there was excellent agreement between RIA and BA; however, at high levels plasma PRL bioactivity exceeded radioimmunoactivity by a small, but significant, amount. A comparison of pituitary PRL concentrations measured by RIA and BA were in good agreement when homogenization was done at pH 10.6. However, when homogenization was done at pH 7.6, slightly but significantly more PRL was extracted when assayed by BA than when assayed by RIA.

Studies on prolactin in human serum, urine and milk.

Prolactin activity was measured in serum, urine and milk using a specific human prolactin radioimmunoassay (RIA). Serum, urine and milk were parallel with the human prolactin standard in the RIA. There was no correlation between serum prolactin levels and urinary prolactin activity. Dialysis of urine samples resulted in complete loss of human prolactin activity while the addition of human prolactin to the urine resulted in the recovery of over 50% of the hormone after dialysis. Thus it was concluded that prolactin is not present in urine. In additional experiments it was observed that the RIA prolactin activity in urine was significantly correlated with the osmolality of the urine and that Na+ and K+ were contributory elements. On the other hand, prolactin was found in human milk and correlated well with the expected serum levels of this hormone. This latter finding is interesting because prolactin receptors have been shown to exist on the serosal side of the mammary epithelial cells. The presence of prolactin in milk suggests the possibility of other sites of action for this hormone in addition to the cell membrane.

The effect of neonatal sex hormone manipulation on the incidence of diabetes in nonobese diabetic mice.

Abstract The nonobese diabetic (NOD) mouse is a model of Type I (insulin-dependent) diabetes. It develops autoimmune pancreatic β-cell lesions characterized by lymphocytic infiltration and β-cell destruction. The incidences of diabetes for male and female NOD mice in our colony were 24% and 73%, respectively. In this study, we investigated the effect of neonatal manipulation of the sex hormone profile on the incidence of diabetes in male and female NOD mice. One day after birth, male mice were castrated and female mice were either ovariectomized, given testosterone, or ovariectomized and given testosterone. The mice were maintained for 140 days and blood samples were collected biweekly starting at 42 days old. Diabetes was determined by three consecutive blood glucose levels > 200 mg/dl. Neonatal gonadectomy increased the incidence of diabetes in males but decreased it in females. Females treated with testosterone also had a decreased incidence of diabetes, whereas ovariectomy plus testosterone increased the incidence to 100%. Castration decreased the body weight in males and increased body weight in females. Testosterone treatment with or without ovariectomy also increased body weight. From these studies, we concluded that neonatal hormonal imprinting has a significant influence on the incidence of diabetes in the NOD mouse.

Influence of Prolactin and Growth Hormone on the Activation of Dwarf Mouse Lymphocytes In Vivo

Abstract The influence of recombinant bovine prolactin (PRL) and recombinant bovine growth hormone (GH) was examined on the popliteal lymph node (PLN) expression of interleukin-2 receptors (IL-2R) in female Snell dwarf mice and normal litter mates after concanavalin A footpad injection. The absolute number of PLN CD4+, CD8+, or B+ cells of dwarf mice was less than that observed for normal litter mates, but when adjusted for the difference in body weight, only the absolute number of B cells was lower in dwarf animals when compared with normal litter mates. The injection of PRL or GH did not alter the observation. The administration of recombinant bovine PRL to normal animals, but not recombinant bovine GH, increased the expression of IL-2R on unstimulated PLN CD4+ and CD8+ subsets. Hormone administration to dwarf animals, however, did not alter the expression of IL-2R on unstimulated PLN T cell subsets. PLN cells from dwarf animals were poorly activated in vivo after injection of concanavalin A and the level of IL-2R expression induced was only 50% of that seen in the PLN of normal animals. The administration of PRL and GH completely corrected the defective induction of IL-2R expression on PLN from dwarf animals after concanavalin A stimulation. These findings strongly suggest that PRL and/or GH play an important role at some stage of the T cell activation process in vivo. Further studies are needed to precisely identify the defect in the dwarf mice.

Milk prolactin is biologically active

Abstract Fat-free milk from cow and goat was chromatographed on Sephadex G-100 and the prolactin (PRL) activity of the fractions determined by radioimmunoassay (RIA). A single prolactin component was observed in 3 cow and 3 goat milk samples with a Vf/Vt ratio of approximately 0.5. Fractions in which PRL was detected by RIA and fractions on either side of the PRL peak were combined, dialyzed and freeze dried. The fractions were assayed for biological activity using the pseudopregnant rabbit mammary gland in organ culture; the degree of secretory response was evaluated histologically. Milk prolactin was biologically active. In the RIA cow milk PRL and one of 2 samples of goat milk PRL gave dose response curves parallel with the bovine PRL standard. In the bioassay the dose response curves for cow milk PRL and ovine PRL were parallel while goat milk PRL was parallel when the results were compared on a weight basis but not on the basis of prolactin content of the preparations assayed by RIA.

Ectopic prolactin secretion from a gonadoblastoma

A 6.5‐year‐old girl developed isosexual, pseudoprecocious puberty secondary to a gonadoblastoma. The tumor was found to produce and secrete both immunoassayable and boiassayable prolactin based on immunohistochemical techniques and the presence of a prolactin gradient between the tumor vein and peripheral vein. The source of the prolactin was a Sertoli‐like cell. Neither growth hormone nor growth hormone‐releasing hormone was detected within the tumor. This case confirms the ectopic production of prolactin by neoplastic tissue.

Prolactin modulates the incidence of diabetes in male and female nod mice

The nonobese diabetic (NOD) mouse develops diabetes spontaneously due to autoimmune destruction of the pancreatic islets with a higher incidence in the female than the male. Prolactin (PRL), a hormone whose role has been previously focused on reproduction and lactation has been demonstrated to influence immune responses. In this study, we investigated the effect of hypoprolactinemia and hyperprolactinemia on the incidence of diabetes in male and female NOD mice. Our hypoprolactinemia model was induced from the time of weaning (21 days of age) to 112 days of age by daily injections of 200 micrograms of bromocriptine (CB-154). A hyperprolactinemic model was induced by a syngeneic anterior pituitary transplant (APT) to the kidney capsule at 35 days of age and maintained until 112 days of age. Additional experimental groups were also investigated. A group of males received pituitary transplants combined with daily subcutaneous injections of CB-154. A group of females treated with CB-154 was also given daily subcutaneous injections of 30 micrograms of oPRL. An ovariectomized (OVX-Control) group of females was also established to serve as a second control for the OVX-APT group. Bromocriptine administration did not significantly decrease plasma PRL levels compared to controls (CTRL) while APT animals had plasma PRL levels that were significantly higher (P < 0.01) than those of CTRL and CB-154 animals. These differences were observed in animals of both sexes. Bromocriptine treatment of APT groups significantly lowered plasma PRL levels from their respective controls. Plasma PRL from the OVX-Control group was markedly lower than the intact female control. The incidence of diabetes was significantly lower in female mice receiving CB-154 injections compared to the intact female CTRL group at 84, 98 and 112 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Restraint Stress Decreases Afternoon Plasma Prolactin Levels in Female Rats. Influence of Neural Antagonists and Agonists on Restraint-Induced Changes in Plasma Prolactin and Corticosterone

Female Sprague-Dawley rats were ovariectomized, given estrogen, and blood samples were obtained via an atrial catheter in the afternoon during the prolactin (PRL) surge. Restraint stress applied at 16.00 h and continued for 3 h resulted in marked decrease in plasma prolactin (PRL) and an increase in plasma corticosterone (B). The neural mechanism(s) involved in the plasma PRL decrease to restraint stress in the afternoon were examined using neural agonists and antagonists. The administration of pimozide, a dopamine antagonist, increased plasma PRL and completely prevented the restraint-induced decrease in PRL. This result suggested that an increase in dopamine secretion mediated the stress-induced decrease of PRL in the afternoon. In unrestrained animals, the intravenous administration of atropine (a muscarinic cholinergic antagonist), arecoline (a muscarinic cholinergic agonist), propranolol (a beta-adrenergic antagonist) and morphine (a beta-endorphin agonist) at 16.00 h decreased plasma PRL from that of vehicle-injected animals. Bicuculline (a GABAergic antagonist) had no effect while phentolamine (an alpha-adrenergic antagonist) and phenoxybenzamine (an alpha-adrenergic antagonist) initially increased and then decreased plasma PRL. Naloxone (a beta-endorphin antagonist) initially decreased and then increased plasma PRL in unrestrained animals. In restrained animals, the intravenous administration of atropine and naloxone had no effect on the decrease in plasma PRL. Bicuculline and propranolol decreased plasma PRL below that observed for restrained animals alone, while phentolamine and morphine slightly retarded the course of the decrease. Arecoline did not alter the PRL decrease to restraint in the early sample periods but was followed by a rebound increase at later times.(ABSTRACT TRUNCATED AT 250 WORDS)