CLINICAL OBSERVATIONS ON CHANGES IN CONCENTRATIONS OF HORMONES IN PLASMA OF 2 STALLIONS WITH THERMALLY-INDUCED TESTICULAR DEGENERATION

To investigate effects of thermally-induced testicular degeneration on hormonal and seminal parameters in stallions, the scrotum was insulat ed for 36 hours in two mature (5-year-old mixed breed and 11-year-old Thoroughbred) stallions. Semen was collected daily for 10 days (DSO) p rior to, and at intervals after, scrotal insulation. When DSO determin ations were not being made, semen was collected 3 times weekly. Jugula r blood samples were collected at 15-minute intervals for 6 hours from each stallion prior to, and at intervals after, scrotal insulation. A mouse interstitial cell testosterone assay was modified to quantify b iologic activity of equine luteinizing hormone (BLH) in plasma samples . Immunoactive luteinizing hormone (ILH) and testosterone (T) concentr ations were determined in plasma samples by routine RIA procedures. Pe rcentages of progressively motile and morphologically normal spermatoz oa began to decrease by 1 to 2 weeks postinsulation, reached nadir val ues at 3 to 3-1/2 weeks postinsulation, and returned to preinsulation values by 7 weeks postinsulation. Total number of spermatozoa and tota l number of progressively motile, morphologically normal spermatozoa i n ejaculates at DSO returned to normal by 8 weeks postinsulation in st allion 2 and 12 weeks postinsulation in stallion 1. Concentrations of BLH and ILH increased, and while T concentrations decreased, immediate ly postinsulation. The increase in ILH concentrations was greater than the increase in BLH concentrations, resulting in a decrease in the BL H:ILH (B:I) ratio. Following the peak in LH secretion immediately post insulation, LH concentrations gradually decreased while T concentratio ns increased. The B:I ratio was elevated from 1 to 13 weeks postinsula tion compared to immediately postinsulation. In addition to changes in spermatozoal quality in ejaculates, stallion response to scrotal insu lation included increased secretion of luteinizing hormone and impaire d Leydig cell function (as determined by reduced testosterone concentr ation in circulating plasma). The proportion of biologically active LH secreted in response to thermal testicular injury increased during th e recovery phase.