ACTION OF CERTAIN HORMONES ON THE THYMUS OF THE DOMESTIC HEN

Abstract

SUMMARY: Thyroxine, deoxycorticosterone acetate (DCA), progesterone, testosterone, oestradiol, cortisone and bovine growth hormone (GH) were injected daily for 4 weeks into laying hens. Thymus weight was increased by thyroxine, decreased by cortisone and unaffected by testosterone and oestradiol. Results with DCA and progesterone were inconclusive but suggested a thymus weightreducing action. GH increased thymus weight but not to a significant degree. Testosterone injected daily for 6 weeks into adult male mallards did not affect thymus weight. Thyroxine and GH increased thickness of the cortex and vascularity of both cortex and medulla of the thymus. Cortisone, DCA and progesterone caused cortical atrophy. Weight of the bursa fabricii was not affected by any of the hormones used. Egg-laying was somewhat reduced by all the hormones used, but this effect was marked only with thyroxine (in one out of two experiments), oestradiol and GH. A moult was induced by thyroxine, testosterone and GH, but the effects obtained with the latter may have been due to contamination with thyrotrophic hormone. It is suggested that the spontaneous late-summer enlargement of the thymus of adult wild birds is due to increased thyroid activity at this time.