Influence of early surgical bursectomy on Leydig cells in the chick embryo testis

Effect of embryonic 19-nortestosterone treatment and surgical bursectomy on plasma concentrations of reproductive hormones, on inhibin content in adrenals and gonads and on the histological appearance of the gonads in the young chicken

Four-day-old chick embryos were hormonally treated with 19-nortestosterone in order to inhibit bursa development. At days 1, 4, 8, 15, 22, 29, and 36 of age, plasma, adrenals, and gonads from intact and hormonal treated chicks were collected. In embryonic nortestosterone treated males the appearance of a left 'ovotestis-like' gonad was observed. The occurrence of this ovotestis-like left gonad in the 19-nortestosterone treated male is probably a secondary effect of the in ovo treatment since surgically bursectomised chicks did not show the testicular morphology and histological changes as observed in 19-nortestosterone treated chicks. Additionally, both male and female hormonally or surgically treated chicks showed relatively enlarged adrenal glands. Hormonal bursectomy affected organ inhibin contents and plasma inhibin, testosterone, and FSH levels in males. Male hormonal treated chicks showed lower levels of plasma inhibin (p=0.0001), testosterone (p=0.01), and FSH (p=0.004), and a lower total testes inhibin content (p=0.0003) compared to intact chicks. However, none of these were significantly different between female intact and hormonal treated chicks, again indicating that the observed hormonal changes in males are not the result of the disappearance of the bursa but of the hormonal 19-NT treatment. The total adrenal inhibin content as well as the adrenal inhibin concentration were significantly higher in hormonally treated chicks than in intact chicks (p=0.0001), regardless of the sex.

Chick gonadogenesis following early surgical bursectomy. I. Histological, morphometric and histochemical data on the embryonic left ovary

Left ovaries of bursectomized chick embryos were examined on the 17th day of incubation in comparison to normal and sham-operated controls, by histological and histochemical observations. The results show that in bursectomized embryos the cortex appears irregularly developed, with a significant decrease in the mean thickness and in the percentage of the secondary sex cords in the total cortical area. Furthermore, the germinal epithelium appears thicker and the subcortical medulla and the tunica albuginea more compact. The greater activity of the enzyme delta 5-3 beta-hydroxysteroid dehydrogenase (delta (5)3 beta HSD) found in ovaries of bursectomized embryos (histochemical method) could be related to an endocrine dismetabolism affecting the cortical development. On the basis of these results and those of other authors, some hypotheses are advanced. In particular, an action of the bursal factor on GTH receptors could be the factor responsible of the enhanced steroidogenic activity altering the hormonal environment.

In vivo and in vitro inhibition of human chorionic gonadotropin-induced testosterone production in rat testis by bursa of fabricius extract

A bursa of Fabricius homogenate extract (BHE) was used to investigate the endocrine regulation function of this avian organ. In vivo and in vitro results indicated that BHE inhibited human chorionic gonadotropin (HCG)-induced testosterone production by rat testes. Leydig cells from collagenase-dispersed rat testes, when treated with BHE, showed a dose-response related depression of testosterone production under HCG stimulation. Young male rats, injected simultaneously with BHE and HCG, failed to show the marked testosterone production peak observed in rats injected with HCG only. However, in vivo treatments with BHE, in the absence of HCG stimulation, did not inhibit basal testosterone production. These results indicate that the bursa of Fabricius produces an endocrine regulation factor that inhibits HCG-induced testosterone production both in vivo and in vitro. Further investigation is necessary to isolate the active factor and determine its mechanism of action.

Interrelation of the avian immune and neuroendocrine systems

Our understanding of immunology and endocrinology has been enriched by studies with different avian species. Numerous experiments have identified the role of the avian thymus and bursa of Fabricius in the immune response and the interrelation of these glands and their cellular products with the neural endocrine system. The growth pattern of the thymus and bursa are influenced by steroids. Increases in thymi growth appear to be controlled, in part, by fluctuations in thyroid activity. Sex-linked dwarf (SLD) chicks have lower T3 levels than normal chicks, but normal levels of growth hormone. The poor agglutinin response of SLD chickens to low concentrations of sheep red blood cells (0.1-1.0%) may be overcome by increasing the percentage of sheep erythrocytes to 5 or injecting growth hormone, which may enhance the conversion of T4 to T3. Castration impaired cell-mediated immunity but surgical removal of the thyroid did not significantly influence the humoral response to sheep erythrocytes or Brucella. Embryonic hypophysectomy reduced the number of B cells in the late embryo. Lesioning the anterior pituitary in 9-day-old chicks markedly reduced several parameters of cell-mediated immunity. In ovo bursectomy at 68 hr markedly increased the size of the adrenals and testes, numbers of Leydig cells, and levels of circulating testosterone but not corticosterone. On the basis of identification of lymphokines or cytoplasmic granules, lymphocytes and other cells of the lymphomyeloid complex are candidates for an endocrine role. A circuitry between the lymphocyte and neuroendocrine system has been identified in mammals and should be extended to Aves.