Altered pituitary hormone response to naloxone in hypertension development.

Abstract

Endogenous opioid regulation of blood pressure is altered during stress in young adults at risk for hypertension. We studied the effects of the opioid antagonist naloxone on the secretion of corticotropin and /3-endorphin during psychological stress in young adults with mildly elevated casual arterial pressures. Naloxone-induced secretion of both corticotropin and 0-endorphin was significantly diminished in persons at enhanced risk for hypertension compared with the low blood pressure control group. Results suggest that opioidergic inhibition of anterior pituitary function is altered in hypertension development. {Hypertension 1989;14:636-644) E ndogenous opioids interact with circulatory control nuclei at several distinct anatomic sites, including adrenal medullae and peripheral sympathetic ganglia, 1-2 nucleus tractus soli-tarius, 3 and hypothalamic paraventricular nuclei. 4-5 This multiplicity of pathways results in pressor or depressor actions of opioid antagonists, depending on the dose, site of action, behavioral state, and the species under investigation. 6-8 Recent work with the stereospecific opioid antagonist naloxone suggests diminished opioid inhibition of circulatory responses during stress in young adults with blood pressure dysregulation and enhanced risk for essential hypertension. 9 Pretreatment with naloxone poten-tiates blood pressure responses during mild psychological stress in persons with low casual blood pressure, but has no pressor effect in persons with high casual blood pressure. This diminished pressor effect of naloxone is not observed during orthostatic challenges, suggesting that the altered opio-inhibitory mechanism of blood pressure control in hypertension development occurs in circuitry that is parallel with or rostral to baroreceptor reflex pathways. 10 The hypothalamo-pituitary-adrenocortical and sym-pathoadrenomedullary axes are both apparently regulated by opioidergic input, and this may be important in the development of essential hypertension. Corticotropin releasing factor (CRF) cell bodies in hypothalamic paraventricular nuclei are believed to stimulate central autonomic efferents as well as secretion of corticotropiri (ACTH), 4-5 but the functional relation between these two effector systems in essential hypertension remains obscure. Naloxone-induced stimulation of plasma ACTH and epineph-rine concentrations in humans 11-12 suggests hypotha-lamic opioid integration of stress-related pressor mechanisms. We now present data that suggest that opioidergic inhibition of anterior pituitary function is altered in young adults at risk for hypertension. Subjects and Methods The experimental protocol was divided into two parts: 1) an on-campus blood pressure screening and 2) the placebo-controlled, in-laboratory stress tests. Two hundred Duke University undergraduate men between 18 and 24 years of age participated in a casual blood pressure screening at the student activity center on campus. Subjects with a history of major medical problems or who were receiving prescription medic...

Naloxone does not influence cardiovascular responses to mild mental stress in postmenopausal women

“…However, the cardiovascular findings of this study are in contrast to previous results in men (7,25,28) showing enhanced hemodynamic responses to acute stress after opioid blockade. The lack of an influence of naloxone on cardiovascular responses in our study might be attributed to different dosage used.…”

“…On the other hand, this study demonstrated in both groups a significant increase in serum cortisol concentrations in response to naloxone. This result confirms for postmenopausal women the inhibitory effect of the endogenous opioid system on the HPA axis observed in other studies for younger women and men (10,15,25). As these responses were unrelated to HRT use, the opioidergic regulation of the HPA axis seems, in contrast to the HPG axis, not to be dependent on sex steroids.…”

“…The lack of an influence of naloxone on cardiovascular responses in our study might be attributed to different dosage used. However, similar doses were used in many other studies, irrespective of the study design (10,13,14,16,25). Therefore, and because of effects on the HPA and HPG axis, it is rather unlikely that dosage might have been too low to detect an effect of naloxone on cardiovascular measures.…”

“…Women were randomized to receive intravenous infusions of naloxone (0.1 mg/kg over 10 min, Narcanti, Du Pont Pharma, Bad Homburg, BRD) or PSS as placebo on 2 different days with a wash-out period of 7-14 days. The dosage of naloxone was selected to inhibit hormonal and hemodynamic opioid actions in the absence of side effects (25). Testing was identical on the 2 study days ( Fig.…”

“…Studies have suggested a dampening role of the opioidergic system on cardiovascular stress responses. Activated by mental stress the central opioidergic system is supposed to exert a phasic inhibition on the hypothalamic-pituitary-adrenal (HPA) and the hypothalamo-sympathetic axis, as the nonselective opioid antagonist naloxone enhances catecholamine and cardiovascular responses to mental stress (7,18,25,28). Furthermore, a tonic inhibitory action of central ␤-endorphin on pituitary proopiomelanocortin (POMC)-related peptides via inhibition of corticotropin-releasing hormone (CRH) release was assumed from increases in plasma adrenocorticotropin (ACTH) and ␤-endorphin after naloxone infusion (4,10).…”