Eiichi Ooya

Endothelin-3 stimulates the hypothalamic-pituitary-adrenal axis

Endothelin-3 (ET-3) is a member of the novel vasoconstrictive peptide family, identified in porcine central nervous system. Intravenous bolus injection of 1000 pmol/kg of ET-3 in freely moving rats caused significant increases in plasma ACTH and corticosterone levels, almost equivalent to those of 100 pmol/kg of rat corticotropin-releasing hormone (rCRH). The action of ET-3 was virtually abolished by pretreatment of CRH-antagonist, alpha-helical CRH. When ET-3 was added to cultured anterior pituitary cells, neither direct stimulation of ACTH release nor potentiation of rCRH action was noted. The results indicate that ET-3 may function as a neuropeptide and stimulation of the CRH-neurons, direct or inderect, is mainly responsible for activation of ACTH and corticosterone release.

Effects of neonatal treatment with monosodium glutamate on circadian locomotor rhythm in the rat

In order to study the effects of treatment with monosodium glutamate (MSG) during the neonatal period on the intrinsic circadian timekeeping system in rats, the locomotor activity of blinded MSG-treated and control (saline-treated) rats was analyzed with power spectral analysis and cross-correlation. In contrast to a robust free-running circadian rhythm in the control rats, a significant shortening of the circadian period and rapid decomposition into ultradian components were noted in the MSG-treated rats. Computer-assisted stereometry of the hypothalamic nuclei revealed that, in addition to the well-known severe damage in the arcuate nuclei (ARC), the volumes of the suprachiasmatic nuclei (SCN) and ventromedial hypothalamic nuclei (VMH) were also reduced significantly in the MSG-treated rats. Although no gross histological damage was apparent in either the SCN and VMH, neonatal MSG treatment appears to impair the function of SCN to integrate many minor oscillations in the brain into a single, definite and precise circadian period.

Stimulation of the hypothalamic-pituitary-adrenal axis by epidermal growth factor

The effects of mouse epidermal growth factor (mEGF) on the hypothalamic-pituitary-adrenocortical axis were studied in vivo in conscious male rats and in vitro with cultured anterior pituitary cells. Both intravenous (i.v.) and intracerebroventricular (i.c.v.) injections of mEGF (5-20 ng: 8.3-33.3 pmol) produced significant, dose-related increases in plasma ACTH and corticosterone concentrations. The potency of mEGF is 1/20-1/50 of that of rat corticotropin-releasing factor (rCRF), and pretreatment with 150 micrograms alpha-helical CRF (9-41) completely abolished the effects of the two peptides. mEGF in concentrations ranging from 10 pM to 10 nM did not significantly affect ACTH release from dispersed anterior pituitary cells. It also failed to alter ACTH secretion in response to rCRF. These results indicate that mEGF stimulates the pituitary-adrenocortical axis through a CRF-dependent mechanism.

Effect of Intrahypothalamic Implantation of Cortisone Acetate on the Onset of Circadian Corticosterone Rhythm in Neonatal Female Rats

Subcutaneous administration of corticosteroids to neonatal rats has been reported to delay the onset of the circadian corticosterone rhythm. Micropellets of a cortisone acetate(CA)-paraffin mixture or paraffin alone were implanted intrahypothalamically or subcutaneously in 2-day-old female rats. 24- or 48-hour patterns of blood corticosterone were obtained serially in individual rats at 21, 28, 35, 56 and 120 days of age. Sham(paraffin)-implanted rats and those bearing CA pellets subcutaneously showed a well-defined circadian corticosterone rhythm at day 28. CA implantation into the anterior hypothalamus, however, caused a delay in the onset of the circadian corticosterone rhythm by 1 week together with a diminished amplitude. In rats with CA pellets in the medial basal hypothalamus, the corticosterone rhythm was not fully established even on day 56, but was evident in most animals on day 120. It is suggested that neonatal CA treatment exerts its effect by inhibiting the maturation of the efferent neural pathways carrying circadian signals from the suprachiasmatic nuclei.

Negative Feedback by Corticosterone is the Major Mechanism Responsible for Corticotropin‐Releasing Factor‐Induced Desensitization

Subcutaneous infusion of ovine corticotropin‐releasing factor (oCRF) to male rats at a rate of 0.1 μg/h for 4 days did not alter the rise of plasma adrenocorticotropin (ACTH) and corticosterone induced by 3‐min ether exposure. In contrast, 1.0 μg/h oCRF for 4 days virtually abolished the ACTH response to ether, whereas a substantial corticosterone response was preserved. Intravenous administration of phenoxybenzamine (5 mg/kg) prior to ether stress completely inhibited the corticosterone response. Plasma ACTH and corticosterone responses in chronic CRF‐treated rats to an intravenous bolus injection of 2.0 μg oCRF were also markedly blunted by pretreatment with subcutaneous oCRF 1.0 μg/h for 4 days. Adrenalectomized rats given corticosterone in the drinking fluid at a concentration of 80 μg/ml showed a plasma corticosterone pattern mimicking the normal diurnal rhythm. Basal plasma ACTH and thymus weight were within normal limits. In these rats, the magnitude of ACTH rise to ether stress did not differ between the chronic CRF‐treated rats and the vehicle‐treated rats. In cultured pituitary cells prepared from animals infused with oCRF 1.0 μg/h for 4 days, the basal and CRF‐stimulated ACTH release was reduced by 46%. We conclude that among the possible mechanisms proposed for ‘desensitization’ during long‐term infusion of CRF, negative feedback by elevated corticosterone at both brain and pituitary levels is the primary factor. The results also suggest the existence of non‐ACTH‐mediated catecholaminergic systems in the stress‐induced adrenocortical activation.

Normoreninemic Hypoaldosteronism in a Case of Isolated ACTH Deficiency

This paper documents the rare and hitherto unreported association between isolated ACTH deficiency and normoreninemic hypoaldosteronism in a 63-year-old woman. Baseline plasma aldosterone and 18-hydroxycorticosterone were extremely low. Both steroids did not respond to exogenous angiotensin II infusion, whereas they were increased in parallel to ACTH stimulation. Thus, acquired dysfunction or congenital dysgenesis of the zona glomerulosa was suspected. The upright posture-furosemide test showed a subnormal but definite plasma aldosterone response coupled with a normal increase in plasma renin activity, indicating that there may be a yet unidentified mechanism(s) underlying the postural increase of aldosterone.

エンドセリンはCorticotropin-Releasing-Hormoneを介してACTH分泌を刺激する

Endothelin 3 (ET3) is a member of the novel vasoconstrictive peptide family, identified in the porcine central nervous system. The effect of ET3 on the hypothalamic-pituitary-adrenal axis in male rats was examined in vivo and in vitro. Intravenous bolus injection of 1000pmol/kg of ET3 in free moving rats caused significant increases in plasma ACTH and corticosterone levels, almost equivalent to those of 100pmol/kg of rat corticotropin-releasing hormone (rCRH). Since an iv bolus injection of ET3 1000pmol/kg did not cause significant changes in the blood pressure of anesthetized rats or the locomotor activity of free moving rats, it seems unlikely that ET3 1000pmol/kg acted as a nonspecific stressor. When ET3 (10(-11) greater than 10(-7)M) was added to cultured anterior pituitary cells, neither direct stimulation of ACTH release nor potentiation of rCRH action was noted. Although it has been shown that ET3 administered systemically probably does not cross the brain-blood-barrier, circulating ET3 may reach the brain tissues through regions lacking the tight barrier, circumventricular structures. The next studies included pretreatment of antagonists or blockers of ACTH stimulating hormones to elucidate the mechanisms of ET3 induced ACTH release. The action of ET3 was virtually abolished by pretreatment of CRH-antagonist alpha helical CRH (150 micrograms/rat icv). But pretreatment of catecholamine-blocker alpha methyl-tyrosine (100mg/kg iv), arginine vasopressin-antagonist dP-thy(Me)AVP (50 micrograms/rat iv) and prostaglandin-blocker indomethacin (3mg/rat iv) did not inhibit the action of ET3. The results indicate that ET3 may play the role of a neuropeptide and that the stimulation of the CRH-neurons is mainly responsible for activation of ACTH and corticosterone release.