IN-UTERO AND LACTATIONAL EXPOSURE OF THE MALE HOLTZMAN RAT TO 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN - DECREASED EPIDIDYMAL AND EJACULATED SPERM NUMBERS WITHOUT ALTERATIONS IN SPERM TRANSIT RATE

Decreased daily sperm production (DSP) and cauda epididymal sperm numb er (CESN) are some of the most sensitive effects of in utero and lacta tional 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure. The reduct ion in CESN cannot be fully accounted for by decreased spermatogenesis . To explain the decrease in CESN it was hypothesized that TCDD exposu re increases the rate of sperm transit through the excurrent duct syst em, thereby decreasing the number of sperm in the system at any given time, Pregnant Holtzman rats were administered a single dose of TCDD ( 1.0 mu g/kg, po) or vehicle on gestation day 15 and offspring were wea ned on postnatal day (PND) 21, On PND 50, testicular sperm were labele d in five males per litter, from 30 control and 26 TCDD-exposed litter s, by injecting 15 mu Ci [H-3]thymidine into each testis, under genera l anesthesia. Sperm movement through the excurrent duct system was mon itored daily 35-64 days post [H-3]thymidine injection. On PNDs 92-93, TCDD exposure significantly decreased DSP/testis, corpus and cauda epi didymis sperm numbers, vas deferens sperm number, and ejaculated sperm number by 28, 30, 36, 39, and 46%, respectively. The decreases in spe rm number in the distal excurrent duct system were greater than the de crease in DSP, consistent with the hypothesis that TCDD exposure cause s an effect other than decreased DSP that reduced epididymal and ejacu lated sperm numbers, However, in utero and lactational TCDD exposure d id not alter radiolabeled sperm transit time through the whole epididy mis (15 days), With TCDD exposure causing no obvious alteration in spe rm transit rate, a plausible explanation for the sperm loss is an incr ease in sperm phagocytosis in the excurrent duct system. (C) 1996 Acad emic Press, Inc.