Changes in concentration of serum prolactin during social and reproductive development of the spotted hyaena (Crocuta crocuta).

A homologous radioimmunoassay system developed for humans was used to measure prolactin concentrations in spotted hyaenas. Concentrations of prolactin showed a significant (P < 0.05) decrease in lactating females, which is consistent with the infrequent suckling pattern of this species. This lack of hyperprolactinaemic conditions during lactation may explain the ability of females to resume reproductive activity soon after the loss of a litter, or even during lactation. Prolactin concentrations did not increase significantly during dispersion in male spotted hyaenas. This conforms to the pattern observed for cortisol, but differs from that for androgen, which fluctuates significantly with social suppression. Although comparative data from other species provide some circumstantial evidence for hyperprolactinaemic conditions during male dispersal, no obvious deductions regarding the recorded inverse relationship between prolactin and cortisol concentrations in mature males could be made.