Response of prolactin to hemorrhage is similar to that of adrenocorticotropin in swine

Abstract

Prolactin (PRL) responds to several stimuli that elicit release of adrenocorticotropin (ACTH), but does not increase in response to hemorrhage in fetal animals. To determine whether PRL increases after hemorrhage in older animals, 11 immature female swine were prepared chronically under halothane and conditioned behaviorally to lie in a sling. They were bled 14 ml/kg over 5 min. PRL, ACTH, cortisol (F), lysine vasopressin (LVP), and pressure renin activity (PRA) were measured by radioimmunoassay. Epinephrine (EPI) and norepinephrine (NE) were separated by high-performance liquid chromatography. Arterial PRL increased at 0.75 and 1 h (P less than 0.01) and paralleled ACTH and F that peaked at 0.75 h (P less than 0.05 and P less than 0.01, respectively). All three hormones recovered significantly by 4 h. In contrast, PRA and LVP peaked transiently at 0.25 h after hemorrhage and recovered by 1.5 h (P less than 0.05, in each case). EPI and NE did not change significantly. In individual pigs, ACTH and F each showed correlations (Spearman) with PRL that were positive in 10 pigs and significant in six and five pigs, respectively. The pig with the smallest ACTH change (8.4 pg/ml peak) showed no increase in PRL. Peaks in PRL were simultaneous with (five pigs) or delayed by 15 min (four pigs) or 30 min (one pig) from peaks in ACTH. Significant correlations of PRL with PRA and with LVP occurred in only two pigs and in one pig, respectively. A common pathway may contribute to other independent mechanisms controlling the release of ACTH and PRL after hemorrhage.