Hiroshi Tomogane

Diurnal patterns of food intake and plasma corticosterone levels in lactating rats

Abstract The diurnal patterns of food intake and plasma corticosterone levels were determined in lactating Wistar-Imamichi rats maintained in a light (14 L: 10 D, lights on 0500 hr) and temperature (24±2°C) controlled animal room. Lactating mothers with four or more than eight pups showed a characteristic diurnal pattern of food intake with high rates of intake around the time of lights off. The diurnal rhythmicity of food intake seemed to disappear in late lactation in mothers with more than eight pups. The plasma corticosterone concentration on day 9 of lactation displayed a diurnal rhythm with high values at 1700 hr and 2100 hr. The rhythmicity of the corticosterone levels was abolished on day 16 of lactation and a high level was maintained throughout a 24 hr period. Since the diurnal rhythm of the corticosterone level was shifted in animals fed during the restricted period (0900–1700 hr) from days 2 to 9 of lactation, the appearance of diurnal rhythm of corticoid secretion seemed to depend on the diurnal feeding rhythm in lactation as well as in the estrous cycle.

Effects of Progesterone on Concentrations of Monoamines in Hypothalamic Areas and Plasma Prolactin Levels in Rats

Abstract The role of progesterone to increase prolactin (PRL) secretion on the first estrous day in pubertal rats was compared with its role in adult cyclic rats. The first estrus was induced by the administration of pregnant mare serum gonadotrophin (5 IU) at 28 days of age. A subcutaneous administration of 2.5 or 7.5 mg of progesterone/100 g body wt significantly increased the concentration of plasma PRL in pubertal rats within 4 hr. The PRL level obtained after progesterone administration was greater than that in similarly treated adult rats. The concentration of dopamine in the arcuate nucleus-median eminence (ARC-ME) in pubertal rats significantly decreased after a lower dosage of progesterone was administered, but no change was found in the preoptic area concentration. In adult estrous rats, the concentration of dopamine in the ARC-ME showed a tendency to decrease after the administration of a larger dose of progesterone (7.5 mg/100 g body wt). No change was observed in the concentrations of indoleamines in the preoptic area and ARC-ME after the administration of progesterone in both pubertal and adult rats. The concentrations of dopamine in the preoptic area and ARC-ME were lower in pubertal rats than in adults. The concentration of 5-hydroxyindole acetic acid and the ratio of 5-hydroxyindole acetic acid to 5-hydroxytryptamine in the ARC-ME were higher in pubertal rats than in adults. These results indicate that progesterone causes a greater increase in tonic PRL secretion in pubertal rats than in adult rats and that a lower hypothalamic dopamine activity and a higher serotonin activity in pubertal rats may account for these differences.

Enhancement of the response of hen granulosa cells to LH with norepinephrine in vitro.

1. The effect of norepinephrine (NE) on progesterone production in hen granulosa cells was examined. After 4 days of the culture, the progesterone production was stimulated by chicken LH but not by NE during a 4 hr incubation. 2. The LH-stimulation progesterone production was not affected by the presence of NE when given together with LH, but was significantly increased when the cells were precultured with NE for 2 days. 3. The effect of NE was inhibited by phentolamine, but not by propranolol. 4. The results indicate that NE may enhance the responsiveness of the hen granulosa cell to LH through alpha-adrenergic receptors.

Ergocornine Blockade of the Surge of Prolactin at Proestrus Failed to Block Ovulation in Cycling Rats

Summary A study was made of the effects of ergocornine methanesulfonate (ECO) administered to normal cycling rats on the afternoon (16.30 hr) of D2 (day before PE) and on the morning (10.30 hr) of PE on prolactin content and concentration of the pituitary gland and on ovulation. Pituitary prolactin content and concentration on the afternoon of PE in the animals treated with ECO were about 3 times higher than those obtained in the saline-treated control animals. When animals treated with ECO were killed on the morning of estrus, the level of prolactin content and concentration was very high and the level was not significantly different from that obtained in the saline-treated control animals killed at the same stages of the estrous cycle. Ovulation occurred in 5 out of 6 animals treated with ECO. No significant difference was obtained in the average number of ova shed between the ECO treated animals and the saline-treated controls. A possible physiological role of prolactin release around the critical period was discussed.