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S. F. Pang and F. Tang


Male and female mice and hamsters were decapitated 1–5 days after birth and serum concentrations of testosterone determined by radioimmunoassay. In the two species studied, serum levels of testosterone in male pups were significantly (P <0·05) higher than those obtained in female neonates. This lends support to the hypothesis that circulating levels of testosterone play an important role in the process of neural sexual differentiation in rodents. Moreover, the sex differences in serum concentrations of testosterone in neonatal rodents together with the detectable levels of testosterone in female neonates may suggest that androgenization is a dose-dependent phenomenon. Alternatively, they may indicate that a minimum concentration of the steroid must be present for androgenization to occur during the critical period of neural sexual differentiation and that this 'threshold' is exceeded in male but not in female rodents.

J. Endocr. (1984) 100, 7–11

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Wolfson Laboratory for Research in Gerontology, Department of Zoology, University of Hull, Hull, HU6 7RX

(Received 20 June 1977)

A relative lack of adrenocortical responsiveness to stress has been described in the rat during the period from day 2 to about day 16 of neonatal life (Schapiro, Geller & Eiduson, 1962; Levine, Glick & Nakane, 1967; Corte & Yasumura, 1975) and the reports to date seem to implicate a lack of response of the pituitary gland as the primary cause (Zarrow, Philpott & Denenberg, 1968; Donovan, 1970; Corte & Yasumura, 1975). Since very little work has been done on the response of the pituitary gland to stress in the neonatal rat, the present study was undertaken.

Female Sprague–Dawley rats weighing 300 g were housed at 22 °C with a light : darkness cycle of 12 : 12 h. Mated female rats were isolated on day 1 of pregnancy, and after

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Wolfson Laboratory for Research in Gerontology, Department of Zoology, University of Hull, Hull, HU6 7RX

(Received 5 April 1911)

Jones, Brush & Neame (1972) reported that the level of adrenocorticotrophin (ACTH) in the plasma returned to the control value as early as 10 min after sham adrenalectomy. In contrast, Cook, Kendall, Greer & Kramer (1973) observed no decline in the level of radioimmunoreactive ACTH in the plasma until 40 min after the onset of a 2·5 min ether stress. Furthermore, the stress levels of ACTH were maintained for 2 h in animals subjected to continual ether stress. Therefore, the levels of both ACTH and corticosterone in sequential samples of plasma from control and dexamethasone-treated rats were measured, in order to see whether a negative feedback mechanism, that acts on the pituitary gland as the level of corticosterone increases, operates even in the presence of continuous stress.

Blood samples were taken

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H. S. YU, S. F. PANG, and P. L. TANG

To study the short- and long-term effects of pinealectomy on the level of retinal melatonin, male rats adapted to a photoperiod of 12 h light: 12 h darkness (with lights on at 06.00 h) were pinealectomized. In the short-term experiment, the rats were decapitated 1 week after pinealectomy. In the long-term experiment, 1 month was allowed for recovery. Melatonin was extracted from retinae and quantified by radioimmunoassay. A diurnal rhythm of retinal melatonin was found to persist after pinealectomy in both experiments. An increase in retinal melatonin was demonstrated 1 month after pinealectomy, indicating a compensatory effect on melatonin in the retinae of pinealectomized rats. Thus, biosynthesis of melatonin in the retina may be modulated through a negative feedback system.

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BM Cheung, IS Hwang, CY Li, WS O, KW Tsang, RY Leung, CR Kumana, and F Tang

Adrenomedullin (AM) is a peptide involved in cardiovascular homeostasis and in inflammation. We examined its expression in a rat model of endotoxaemia. Male Sprague-Dawley rats received intraperitoneal injection of 5 or 10 mg/kg lipopolysaccharide (LPS), or saline as control. Rats were killed at 1, 3, 6, 12 and 24 h after injection. LPS at 5 mg/kg, but not saline, increased plasma AM significantly at 3 h. At 10 mg/kg, plasma AM was raised at 3, 6 and 12 h. Immunoreactive AM concentration in lung increased after 5 or 10 mg/kg LPS, but not saline. PreproAM mRNA level in lung was significantly increased at 3 and 6 h. In conclusion, endotoxin stimulates the expression of AM in the lungs and increases its circulatory concentration. AM may be involved in the systemic response to sepsis.