The Post-Nuptial Occurrence of Progestins in the Seminiferous Tubules of Birds

Abstract

It has been previously suggested that the cholesterol which appears during the post-nuptial metamorphosis of the seminiferous tubules of submammalian vertebrates may be of endocrine significance. It is now shown by means of paper chromatography that the tubular lipids of pigeons probably contain progesterone and its metabolites. The testes of control ('pre-nuptial') birds contain androgens but no progestins.Again, the Hooker-Forbes bioassay test indicates the presence of plasma progestins in seven out of eight birds with metamorphosed lipoidal tubules. Of seven control birds in full spermatogenesis six were negative for progestin. The possibility that the regular, post-nuptial accumulation and expenditure of tubular cholesterol is functionally homologous with the formation and regression of the corpus luteum is discussed.At the end of the seasonal spermatogenesis the seminiferous tubules of wild birds undergo a metamorphosis involving a massive steatogenesis and the profuse appear¬ ance of cholesterol. During the succeeding months the tubular lipids and their cholesterol disappear, the rate varying from species to species [Marshall, 1949[Marshall, , 1950. Since cholesterol is associated with the production of steroid hormones in the neighbouring interstitium, and probably in the adrenal cortex, it may be equally so when quantities of it appear suddenly and cyclically in the seminiferous tubules, and then disappear. In short, the metamorphosed tubules may have a temporary endo¬ crine function.

The Photorefractory Period of the House Finch

“…Such reasoning has prematurely directed attention to the hypothalamus as· the site of photorefractoriness and has left untested at least two reasonable alternative possibilities that involve the testes. These are 1) that the testes, by the positive feedback effect of testosterone, cause termination of photorefractoriness, or 2) that the testes, by production of an inhibitor (perhaps progesterone, Lofts and Marshall 1959), maintain photorefractoriness. The first of these not exhaustive possibilities suggests that a photorefractive process (perhaps in the hypothalamus or pituitary) is terminated by the production of testosterone.…”

Avian Physiology

“…The sertoli cells and the epithelial lining of the excurrent ducts of the testes also contain androgenmetabolizing enzymes (Lofts and Bern, 1972;Tingari, 1973). There are two possible explanations for the occurrence of steroid synthesis in these tissues: (1) the cells have endocrine function in that they produce and secrete androgens to be used by some target tissue (such as the spermatozoa); (2) the sertoli cells and excurrent ducts are target tissues in which metabolism is a function of steroid utilization.…”

Role of gonadal hormones in incubation behavior of male ring doves (Streptopelia risoria).

“…The two known sources of progesterone in males are the adrenal (Beall & Reichstein, 1938;Feder & Ruf, 1969;Holzbauer, Newport, Birmingham, & Traikov, 1969;Resko, 1969) and the gonadal (Lofts & Marshall, 1959;Savard & Goldzieher, 1960) glands. If a progestin acting alone or in synergy with testosterone mediates the transition from courtship to incubation behavior in the male dove, it should be possible to delay the initiation of sitting behavior by removing one or both known sources of these steroids.…”