Morning and evening human Leydig cell responses to hCG

Abstract

Abstract. The present 72 h study compares the patterns of 17α-hydroxyprogesterone (17OHP) and testosterone responses to im hCG (40 IU/kg) injected at 09.00 h and on different occasions at 17.00 h in eight normal men. Basal a.m. steroid concentrations were significantly higher for both steroids (15% for testosterone and 52% for 17OHP). A peak (at 2 h and 3 h) and statistically significant nadir (at 5 h, 5.5 h and 6 h) response was found for each steroid in the a.m. studies, but in the p.m. studies the two steroids rose significantly at 2 h and remained plateaued through 6 h. Between 5 h and 6 h, and for the remainder of the morning and evening studies, the respective steroid concentrations and the patterns to the changes were the same. Between 6 h and 24 h both steroids rose further. 17OHP peaked at 24 h and 48 h, 3.2 times basal and declined at 72 h. Testosterone rose further between 24 h and 48 h, and was unchanged at 72 h. At the latter two times it averaged 2.2 fold basal values. hCG was detectable at 1 h, rose progressively to highest levels at 24 h, and declined thereafter — in similar fashion in the a.m. and p.m. studies. The 'peak and nadir' responses occur within the first few hours of gonadotrophin stimulation begun in the morning and appear to be related to the time of day and do not appear to be the result of a biosynthetic block. This suggests a diurnal variation of human Leydig cell response. With intense, probably maximal, testis stimulation each steroid shows the same respective pattern and circulating concentrations between 5 h and 72 h in both the a.m. and p.m. studies.