The effect of bromocryptine-induced hypoprolactinemia on xenogeneic and allogeneic skin graft survival in a mouse model

Bromocryptine-induced hypoprolactinemia produces immunosuppression capable of extending allograft survival in solid organ transplantation models, but its potential for delaying either xenogeneic or allogeneic skin graft rejection is as yet undefined. In this study the ability of bromocryptine to prolong the survival of either cutaneous human xenografts or murine allografts was compared with cyclosporin A in a mouse model. In xenograft experiments cryopreserved human cadaver skin was grafted to B6D2F1 mice. In allograft experiments skin graft donors (A/J mice) differed genetically from recipients (Balb-C mice) at the major histocompatibility locus. In the untreated control group xenograft survival averaged 7 days and allograft survival 8 days. Xenograft rejection was delayed significantly and nearly equally by both bromocryptine and cyclosporin A (mean 15 and 16 days, respectively). However, allograft rejection was delayed longer by cyclosporin A (mean 24 days; p = 0.0002) than by bromocryptine (mean 15 days; p = 0.066). Administration of porcine prolactin (1 mg) partially reversed the bromocryptine effect (mean xenograft survival, 11 days; mean allograft survival, 10 days). The results of this study suggest that the immunosuppression of prolactin release by bromocryptine may be an effective, benign means of prolonging the survival of biologic dressings (e.g., banked cadaver allograft or porcine xenograft) used for temporary wound coverage in massively burned patients.

Prolactin and prolactin secretagogues reverse immunosuppression in mice treated with cysteamine, glucocorticoids, or cyclosporin-A

Suppression of prolactin (PRL) secretion with the dopamine agonist, bromocriptine, has been shown in rodents to diminish a variety of immunologic responses, including delayed type hypersensitivity, primary antibody response, T-cell dependent macrophage activation, and ex vivo T- and B-lymphocyte proliferation in response to mitogens. These same responses can be suppressed by endogenous or exogenous glucocorticosteroids and, in large measure, the immunosuppressant peptide cyclosporin A. The sulfhydryl reducing agent cysteamine (2-aminoethanethiol) is known to reduce pituitary and plasma prolactin levels. Treatment of mice with cysteamine at doses which suppressed circulating PRL levels resulted in suppression of ex vivo blastogenic responses of lymphocytes from treated mice. The T-cell-dependent primary IgM response to immunization with sheep red blood cells was also suppressed by cysteamine treatment. Treatment of mice with drugs stimulating the release of endogenous PRL, or with exogenous ovine PRL, was found to antagonize the suppression of lymphocyte proliferative responses to mitogens induced in mice by glucocorticoid or cyclosporin treatment. These data suggest that many drugs in common clinical use could have potential immunomodulatory actions due to suppression or stimulation of pituitary PRL secretion. Furthermore, lactogenic hormones appear to exert counterregulatory actions which may modify glucocorticosteroid actions on immune and other target issues.

Endotoxin-induced hypocalcemia results in defective calcium mobilization in rats

Hypocalcemia is common in critically ill patients with sepsis; however, its etiology remains unclear. We have previously reported that hypocalcemia occurs in approximately 20% of patients with gram-negative septicemia. Based upon this finding, we evaluated the effect of endotoxin on calcium homeostasis in laboratory animals. We report here that endotoxin produces a dose-related decrease in circulating ionized calcium levels and impairs calcium mobilization during ethylenebis (oxyethylenenitrilo)-tetraacetic acid infusion. We conclude that endotoxin or its products can cause ionized hypocalcemia during sepsis by impairing calcium mobilization.

Verapamil reverses calcium cardiotoxicity

High circulating concentrations of calcium are toxic to the heart and may cause cardiac arrhythmias and arrest. To investigate the therapeutic use of calcium antagonists in hypercalcemia, we evaluated the efficacy of verapamil hydrochloride and magnesium chloride in the treatment of experimental calcium-induced cardiac arrest in laboratory rats. Verapamil rapidly reversed the experimental calcium-induced arrest and improved survival (83% survival versus 0% in controls). Magnesium failed to reverse this toxic event. We conclude from these experimental studies that verapamil may be useful in the treatment of hypercalcemic cardiac toxicity.

Glucagon is an antagonist of morphine bradycardia and antinociception

Glucagon and its receptors have been identified within the mammalian brain, and their anatomical distribution correlates well with the distribution of opioid peptides and their receptors. To evaluate possible physiological interactions between these two peptidergic systems, we examined the effects of glucagon on two opioid responses - bradycardia and antinociception. Glucagon administered either intravenously (iv) (100-1000 micrograms/kg) or intracerebroventricularly (icv) (5 micrograms) significantly attenuated morphine-induced (200 micrograms/kg, iv) bradycardia without producing any alterations in cardiovascular parameters when given alone. Furthermore, glucagon did not antagonize the bradycardia produced by phenyldiguanide (10 micrograms/kg, iv), a non-opioid substance. Peripheral (1 mg/kg, iv) and central (5 micrograms, icv) glucagon pretreatment antagonized morphine-induced (7.5 mg/kg, intraperitoneal) antinociception by 67% and 86%, respectively, at 30 minutes (as determined by the hot plate test). Glucagon treatment alone at these doses did not alter baseline response latencies. In both cases, central injections of glucagon were more effective than iv injections in antagonizing morphine's effects. These findings demonstrate a central action for glucagon and provide the first evidence that this neuropeptide may function as an endogenous antagonist of opioid actions.

Temporal changes in growth hormone, cortisol, and glucose: relation to light onset and behavior

Plasma growth hormone (GH), cortisol, and glucose were measured every 20 min in the last 2 h of a 12-h dark cycle and the first 4 h of a 12-h light cycle in eight environmentally limited rhesus monkeys; additionally, ongoing behavior was scored every 20 min in the last 4 h when the lights in the booths housing the monkeys were on. Episodic fluctuations in levels of GH, cortisol, and glucose occurred. Onset of booth illumination was associated with a significant number of GH secretory bursts (6 of 18), and more than twice as many bursts per hour occurred in the light than in the dark (L:D = 0.44:0.19). The onset of illumination was also associated with significant increases in glucose for the eight animals. In addition, plasma glucose increased concurrently with the onset of 13 of 18 bursts of GH secretion. Monkeys were rated as significantly more alert or aroused when plasma levels of GH and glucose were increasing than when they were decreasing. In contrast plasma cortisol showed small, rhythmic fluctuations over time that did not correlate with booth illumination or degree of behavioral arousal. This latter finding challenges the traditional assumption that cortisol is a sensitive index of behavioral arousal.