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The physiological function of the bursa of Fabricius (bursa), a gland peculiar to young Aves only, is not well established (see Glick, 1960; Perek & Eilat, 1960; Perek & Bedrak, 1962).
This communication presents the findings of a quantitative study in which the responses of three oxidative enzymes of liver and kidney, namely xanthine oxidase, succinoxidase and cytochrome oxidase, were compared in Leghorn cockerels with and without removal of the bursa, following administration of ACTH. Bursectomy was performed at the age of 2 weeks. At the age of 7 weeks thirty-two birds of comparable body weight, half of which were bursectomized, were selected as the experimental groups. To eight birds of each group (Table 1) 1 ml. saline solution per bird was administered, and to the remaining eight, 1 ml. of ACTH† in saline, 10 i.u. per bird. All injections were given intravenously. The birds were killed by cervical dislocation
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ABSTRACT
Key reactions associated with the capacity of the isolated Leydig cell to synthesize testosterone were studied in male rats acclimatized to a hot environment (33–35 °C, 25–40% relative humidity) and controls (20–22 °C, 30–50% relative humidity). The results demonstrate that acclimatization to heat coincides with: (1) a lower number of human chorionic gonadotrophin (hCG) receptors (P<0·01) in the Leydig cell, (2) higher affinity of the Leydig cell for hCG (P < 0·05), (3) lower hCG-stimulated cyclic AMP production (P<0·05) by the Leydig cell and (4) lower capacity of the Leydig cell to synthesize testosterone (P<0·01) after hCG challenge. It is suggested that the major cellular alteration responsible for the decreased testosterone secretion by the Leydig cell lies distal to the step involving the binding of the trophic hormone to its receptor and that heat-acclimatization induces changes in the integrity of the various cellular membranes leading to the impeded function of adenylate cyclase and 17β-hydroxysteroid oxidoreductase.
J. Endocr. (1984) 102, 167–173
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SUMMARY
A single intraperitoneal injection of 2 μg. d-aldosterone monoacetate/g. body weight produced a rapid, but temporary, uncoupling of oxidative phosphorylation in mouse liver mitochondria. This resulted in low P:O ratios in male and female animals of 1·21 and 1·52, respectively. The P:O ratio of females remained somewhat lower than the control levels but there was a progressive improvement in oxidative phosphorylation during the first 24 hr. after the injection leading to P: O ratios similar to those in the controls. Experiments in vitro showed that the uncoupling effects of aldosterone were related to its concentration in the reaction medium. Aldosterone added to fresh rat liver mitochondria, at concentrations of 10−10, 10−7 and 10−4m inhibited phosphorylation by 9·5, 77·1 and 95·1% and lowered P:O ratios to 2·46, 1·66 and 0·41, respectively. These changes in oxidative phosphorylation were not related to alteration in ATPase activity and were independent of mitochondrial electrolyte concentration.
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Serum concentrations of FSH and LH and the hypothalamic content of gonadotrophin releasing hormone (GnRH) were measured by radioimmunoassay in male rats maintained at 35 °C for various periods of time. The results show that heat exposure caused a temporary decrease in serum concentrations of LH and FSH which was associated with comparable changes in the hypothalamic content of GnRH. Histological examination of the adenohypophysis of rats exposed to heat for 42 days disclosed that the gonadotrophs underwent hypertrophy and hyperplasia and appeared more active than those of control rats. The data suggest that in rats exposed to heat for prolonged periods a new steady-state is established through which an adequate serum level of LH is maintained.
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The relationship between the testes and the adenohypophysis in rats exposed to heat was assessed by (1) the determination of adenohypophysial concentrations of FSH, LH and prolactin as well as serum levels of prolactin and testosterone in rats maintained at 35 °C for various periods of time and (2) the elucidation of the responsiveness to stimulation with gonadotrophin releasing hormone (GnRH) or human chorionic gonadotrophin (hCG) of the rat acclimatized for 40 days to a temperature of 35 °C. The results demonstrated that while heat exposure caused a transient change in the concentration of FSH and LH in the adenohypophysis, the level of prolactin increased by twofold within 24 h and remained significantly higher than in control animals. A concurrent significant decrease in the concentrations of prolactin and testosterone in the serum of rats exposed to heat was also observed. Challenging the rat with exogenous GnRH resulted in a significant increase in serum LH and FSH concentrations in control rats and rats exposed to heat, but the magnitude of the rise in LH was greater in the latter group. However, this phenomenon was not accompanied by a rise in serum testosterone concentration in the rat exposed to heat. Challenging the animals with hCG provoked an increase in serum testosterone, but the magnitude of the rise was greater by far in the control rats. It is concluded that exposure of the intact rat to increased environmental temperatures is accompanied by accumulation of prolactin in the lactotrophs, reduced serum prolactin concentration, decreased capacity of the testes to synthesize testosterone and consequently reduced serum testosterone concentration. These phenomena are independent of the capacity of the adenohypophysis to synthesize LH.
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SUMMARY
Testosterone synthesis was studied in Acomys cahirinus by incubation of its testis with radioactive substrates. In comparison with other rodents, the Acomys testis was found to have a lower 17β-hydroxysteroid oxidoreductase activity, whereas the activity of 20α-hydroxysteroid oxidoreductase was high. The accumulation of 5-ene-3β-hydroxy metabolites suggested that biosynthesis proceeded preferentially by the 4-ene route. This was confirmed by the simultaneous incubation of [3H]5-ene-3β-hydroxysteroids and [14C]4-en-3-oxosteroids. The predominant route of biosynthesis would, therefore, appear to be: pregnenolone → progesterone → 17α-hydroxyprogesterone → androstenedione → testosterone.
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Variations in concentrations of LH, GH, prolactin, corticosterone, oestradiol, testosterone and progesterone in serum were followed over a 24 h period (14 h light: 10 h darkness) in laying and broody turkeys and in turkeys suspected of becoming broody (pre-broody hens). In laying hens marked variations in LH and gonadal steroid levels were observed in relation to the ovulatory cycle of the bird. These patterns of hormone secretion were not seen in either group of broody birds. Levels of GH in serum were very variable and showed no correlation with the egg-laying or light: darkness cycle and the concentrations did not differ between the respective physiological states. A nocturnal increase in the concentration of corticosterone in serum was observed in all three groups of turkeys and the concentration was occasionally higher in the pre-broody and broody birds than in the laying hens. The serum prolactin concentration in each group was also very variable and showed no obvious relationship with the ovulatory or photoperiodic cycle. The mean circulating prolactin concentration throughout the 24 h period did not differ significantly between the groups. These results suggest that broodiness in the domestic turkey is not initiated or maintained by enhanced prolactin secretion.
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Diurnal variations in circulating concentrations of LH, GH, prolactin, corticosterone, oestradiol, progesterone and testosterone were followed in laying and broody White Rock domestic fowl. Throughout the 24 h study prolactin concentrations in serum were consistently (two- to fourfold) higher in broody than in laying birds, in which the prolactin level varied with the light: darkness or ovulatory cycles. Concentrations of GH in serum tended to be lower in broody birds but in both groups were very variable and showed no obvious relationship with either the lighting or ovulatory cycles. Broodiness was also characterized by low LH and gonadal steroid levels and by the absence of preovulatory peaks in the serum concentrations of these hormones. A diurnal rhythm in corticosterone was observed in both the laying and broody birds, with high levels during the period of darkness. Corticosterone concentrations were markedly higher in the broody birds than in laying birds during most of the 24 h study. No diurnal rhythm in the blood haematocrit level was observed in either group, although the level was generally lower in broody birds. This difference, however, was insufficient to account for the lower LH and gonadal steroid levels in the broody birds.
The results suggest that prolactin is involved in the initiation or maintenance of broodiness in the fowl and the possibility of an antigonadal role for the hormone is discussed.
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SUMMARY
The metabolism of 3β-hydroxysteroids, in the presence of NADPH, by testicular homogenates of adult rats acclimatized to a hot environment (33–35 °C, 25–40% relative humidity), was compared with that of control and surgically produced cryptorchid testes. Prolonged exposure to a hot environment stimulated the transformation of 3β-hydroxysteroids to 3-oxo-4-ene metabolites, so that relatively large amounts of the latter accumulated. Pregnenolone was metabolized rapidly to progesterone, 17α-hydroxyprogesterone, androstenedione and testosterone. A similar trend was observed in the metabolism of 17α-hydroxypregnenolone. In-vitro synthesis of testosterone in the rat apparently takes place primarily by the 4-ene pathway. The 5-ene-17,20-lyase reaction appears to be rate-limiting. Heat acclimatization does not seem to affect this step. It does, however, seem to enhance the conversion of dehydroepiandrosterone via 5-androstene-3β,17β-diol to testosterone. Enzymic activity was much lower in cryptorchid than in heat-acclimatized testes, where it actually increased, except for 17β-hydroxysteroid oxidoreductase.
Continuous exposure of rats to a high ambient temperature for 4–6 months tended to decrease testosterone concentration in peripheral blood, and retarded growth rate and gonadal size. Histological examination showed atrophied areas in the testes where necrobiosis of the germinal epithelium had occurred. These necrotic foci, unlike those found in cryptorchid testes, were randomly scattered among intact seminiferous tubules in which active spermatogenesis was taking place.
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SUMMARY
Prolonged aldosterone administration to mice was investigated in relation to liver function. Daily injections of 2 μg. d-aldosterone monoacetate/g. body weight for 60 days adversely affected oxidative phosphorylation of liver mitochondria. The value for the P:O ratio of controls, 3·21, dropped to 2·01, 2·86, 2·45 and 2·79 for mice treated with aldosterone for 20, 30, 50 and 60 days, respectively. The impaired oxidative phosphorylation was neither accompanied by an increase in adenosine triphosphatase activity of liver mitochondria nor by a change in plasma transaminases. Corresponding morphological changes were observed in liver parenchyma starting with hydropic degenerations in early lesions, and single cell necrosis accompanied by mitotic activity (regeneration) in advanced lesions. It seems therefore that hyperaldosteronism might be noxious to liver parenchyma and hepatic function.
