Effect of the repetition of PMSG and hCG treatment on the ovulatory response and the number of follicles in adult rats.

Abstract

The effect of repeated treatments of PMSG and hCG on the ovulatory response and the number of follicles were determined using Wistar-Imamichi rats. At 75 (±2) day-old, animals received the 1st treatment with each 20 or 40 IU of PMSG and hCGat 16 (±2) days interval.When rats were treated with 20 (or 40) IU of PMSGandhCG, the number of ova shed per rat decreased markedly from 23.5 (48.4) by the 1st treatment to 9.3 (8.2) by the 3rd treatment (P<0.01 or 0.001). The number of healthy follicles decreased markedly from 336.2 (360.6) to 187.5 (140.3) after the 3rd treatment with 20 (or 40) IU of PMSG (P<0.01 or 0.001). After the 2nd, 3rd or 4th treatment, the number of healthy follicles was signi-ficantly fewer than that in untreated rats at the same ages (P<0.05 to 0.001), except after the 3rd treatment with 20 IU of PMSG and hCG. The number of healthy follicles in un-treated rats decreased with the advance of age. In both untreated and gonadotropin-treated rats, the decrease was more evident in smaller sized healthy follicles.It is suggested that the low ovulatory response following repeated treatmentswith PMSG and hCG is partly due to a poor recruitment of follicles which are responsive to PMSG.