PHOTOPEROID-MEDIATED INCREASES IN SERUM CONCENTRATIONS OF INHIBIN, FOLLICLE-STIMULATING-HORMONE, AND LUTEINIZING-HORMONE ARE ACCENTUATED INADULT SHORTENED-SCROTUM RAMS WITHOUT CORRESPONDING DECREASES IN TESTOSTERONE AND ESTRADIOL

Relationships between ''seasonal'' changes in the secretion of gonadot ropic (FSH, LH) and gonadal feedback (inhibin, testosterone, estradiol ) hormones were examined in the adult ram. Eight Dorset x Leicester x Suffolk rams were kept in photoperiod-controlled rooms for 2 yr and su bjected to alternating 4-mo periods of stimulatory (8 h light) and inh ibitory ( 16 h light) daylengths. The scrota of four rams were shorten ed at the outset to elevate testicular temperature and presumably impa ir inhibin secretion by Sertoli cells. Blood samples were collected se rially from the jugular vein every 3 wk, and scrotal circumference of the four control rams was measured every 2 wk. Testicular recrudescenc e and regression were completed in the second month of the short- and long-day periods, respectively. Mean serum concentrations of testoster one and estradiol varied in synchrony across months (r = 0.42) and wer e similar between the groups of rams, except early in the short-day pe riods when testosterone was 50% lower in the shortened-scrotum rams be cause of smaller ''seasonal'' increases in testosterone pulse amplitud e and baseline concentration. Increases in the secretion of gonadotrop ic hormones during testicular recrudescence were greater in magnitude (FSH) and/or of longer duration (FSH, LH pulse amplitude, and baseline LH) in rams with shortened scrota. In fact, mean FSH concentration wa s an average of 250% higher in the shortened-scrotum vs. the control r ams throughout the last two photoperiod cycles. Mean inhibin concentra tion varied with month in accordance with FSH (r = 0.52) and either re mained normal or was higher than usual (e.g., 55% during testicular re gression) in the shortened-scrotum rams. Results underscore the comple xity of gonadal regulation of LH and FSH secretion in the ram and the need to investigate the feedback role of other testicular hormones.