Effects of exogenous melatonin prior to the breeding season on testis weight and epididymal androgen receptors in rams.

Rams were randomly assigned to an experiment that evaluated effects of treatment (2.5 mg melatonin/d for 45 d vs control; MEL vs CON) in mid-May through June on testis weight and concentration of epididymal androgen receptor in July or September (Sept). Mean testis weight of MEL and CON rams was not different in July (332 vs 283 g), but in Sept was less (P less than .05) for MEL rams than CON rams (268 vs 382 g). Testis weight of MEL rams was less (P less than .05) in Sept than in July. Caput, corpus and cauda epididymal tissues were used to prepare extracts which were analyzed for concentration of dihydrotestosterone (DHT) receptor using a new standard curve method. A standard extract was characterized using four independent 8-point Scatchard analyses and found to contain 6.0 fmol DHT receptor/mg wet tissue (Ka = 3.5 X 10(8).M-1); this extract was used to establish standard curves for assays of unknown samples. Data on concentration of DHT receptors measured by Scatchard analysis and the standard curve method were highly correlated (r = 0.99; P less than .01; n = 8). Concentrations of DHT receptor were not affected by treatment, month of castration, or their interaction. However, for data pooled across treatment and month, concentration (fmol/mg protein) of DHT receptor was greater (P less than .05) in caput or corpus (125 or 122) than in cauda (92) epididymidis. The regional distribution of epididymal DHT receptors in this study confirmed our previous findings.(ABSTRACT TRUNCATED AT 250 WORDS)