Abstract
Ovarian and uterine morphological changes were examined in the maturing Holtzman rat, ages 22β40 days, using routine histological procedures. These findings were then correlated with serum follicle stimulating hormone (FSH) and luteinizing hormone (LH), in an effort to trace the sequence of events involved in the onset of puberty (i.e., the initiation of cyclicity) which occurred most consistently in our rats at 38 days of age. Ovaries exhibited no significant weight increases prior to day 36. However, microscopic changes became apparent as early as day 30, and continued to day 38, the day of the gonadotropin surge. During this time interval, the proportion of large type 6β7 (potentially estrogen secreting follicles) increased dramatically relative to nonβantrum containing follicles. An increasingly hypertrophied and well differentiated theca interna of the larger follicles was also characteristic of this age interval. Closely paralleling the sequence of follicular maturation, quantitative and qualitative increases in all layers of the uterus occurred. As early as day 32, the luminal epithelium had increased some three to fourβfold over earlier age groups. Similarly, the stromal endometrium and myometrium increased significantly at this time. Further increments occurred through day 34, with a leveling off at this time.
Serum FSH showed no significant increases prior to day 38, at which time levels increased some twoβfold over previously existing levels. In contrast, LH remained tonic until days 34 and 36, at which time subthreshold elevations occurred. On day 38, LH rose some 40βfold over preβexisting levels. Serum prolactin followed a similar pattern; levels became detectable at 33 days of age with marked elevations seen on day 35 and on day 38 of age.
From quantitative and qualitative analysis of ovarian and uterine morphology with subsequent correlations to serum gonadotropins over the maturing process, we conclude that the ovary possibly acts as a βZeitgeberβ for the gonadotropin surge and ovulation.