Prolactin Levels in the Western Spotted Skunk: Changes during Pre- and Periimplantation and Effects of Melatonin and Lesions to the Anterior Hypothalamus1

Abstract

Prolactin (PRL) is the primary pituitary hormone responsible for initiating increased function of the corpus luteum and blastocyst implantation in the western spotted skunk. Therefore, we have designed experiments to validate a PRL RIA, characterize the preimplantation profile in PRL secretion, and determine the effects of exogenous melatonin and lesions to the anterior hypothalamic area (AHA) on PRL secretion in the skunk. These objectives were investigated with a heterologous RIA using canine PRL standards and antiserum. Displacement curves of skunk pituitary extract and serum were parallel to the canine PRL standard curve. Growth hormone-releasing hormone injection did not cause a significant change in plasma PRL levels as detected by the assay (p = 0.74). Injection of pimozide increased and bromocriptine decreased plasma PRL levels (p less than 0.05). A seasonal trend in plasma PRL levels was observed during the preimplantation period, with mean concentrations ranging from 5 ng/ml during the period of short day length in January to 17.1 ng/ml during the long day photoperiod in early May. The average date of blastocyst implantation in this study was 2 May (n = 16). Silastic capsules containing melatonin (n = 5) significantly delayed both the seasonal rise in plasma PRL levels and the time of implantation (p less than 0.05) compared to controls with empty capsules (n = 4). Lesions to the AHA (AHAx, n = 5) eliminated these effects of melatonin on both the rise in PRL and time of implantation. PRL levels were highly correlated with progesterone levels (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)