Transient neonatal hypothyroidism alters plasma and testicular sex steroidconcentration tn puberal rats

The stimulatory and inhibitory effects on testicular steroidogenesis of tra nsient neonatal hypothyroidism from day 1 postpartum through different post natal developmental events on testis at puberal age (60 days old) were stud ied in vivo. Hypothyroidism was induced in neonates by feeding the lactatin g mother or directly with 0.05% methimazole (MMI) through drinking water fr om the day of parturition to 10, 15, 30, 40 and 60 days, and were killed at day 60 postpartum. Plasma and testicular interstitial fluid (TIF) progeste rone, testosterone, dihydrotestosterone (DHT) and estradiol concentrations were assessed. Testis weight and volume significantly increased in rats sub jected to 10 and 15 days of hypothyroidism, decreased in rats subjected to 30, 40 and 60 days of hypothyroidism. A consistent increase in Leydig cell number was seen in puberal rats subjected to transient neonatal hypothyroid ism but decreased in 60 days hypothyroid rats. Peritubular myoid cell numbe r was consistently decreased in all experimental rats. Leydig cell diameter decreased consistently in all experimental groups. Persistent hypothyroidi sm (60 days hypothyroid) consistently decreased both plasma and TIF sex ste roids. In transient hypothyroid rats, progesterone concentration decreased in both plasma and TIF. Transient hypothyroidism from birth to day 10 postn atal age maintained normal titre of plasma testosterone, whereas a signific ant increase in TIF testosterone concentration was evident when compared wi th controls. All other groups of rats subjected to transient neonatal hypot hyroidism had consistently low titres of plasma and TIF testosterone. Plasm a DHT concentrations in rats subjected to transient neonatal hypothyroidism remained unaltered. However, TIF DHT increased in 10 days hypothyroids, de creased in 30 and 40 days hypothyroid rats and remained unaltered in 15 day s hypothyroids. Transient hypothyroidism registered normal titres of plasma estradiol in all groups except in 30 days hypothyroids, which registered a n increase, while a consistent increase in TIF estradiol concentration was observed. The present study indicates that transient neonatal hypothyroidis m, when restricted up to 10 days of postnatal life, at puberal age stimulat es testosterone, DHT and estradiol secretion and when extended beyond 10 da ys of postnatal life shifts towards estradiol secretion.