Brain alpha 1-adrenoceptor in the cardiovascular responses to BHT-920 and phenylephrine

Alpha1-adrenergic receptors in human spinal cord: specific localized expression of mRNA encoding alpha1-adrenergic receptor subtypes at four distinct levels

alpha1-Adrenergic receptors (alpha1ARs) are important in lower urinary tract syndromes such as benign prostatic hypertrophy and bladder irritability. Spinal cord alpha1ARs have been postulated to play a role in modulating these diseases, yet alpha1AR subtype (alpha1a, alpha1b, alpha1d) neuronal localization in human spinal cord has not been described. We therefore tested the hypothesis that alpha1AR subtype distribution varies according to specific spinal cord tract and level. In situ hybridization was performed to identify cell bodies containing alpha1AR subtype mRNA at four levels of human spinal cord (cervical enlargement, thoracic, lumbar, sacral). alpha1AR mRNA is present in ventral gray matter only (ventral>dorsal; sacral>lumbar=thoracic>cervical). Signaling cell bodies were detected in anterior horn motor neurons at all levels; dorsal nucleus of Clarke and intermediolateral columns in cervical enlargement, thoracic and lumbar spinal cord regions; and parasympathetic nucleus in sacral spinal cord. Although all three alpha1AR subtypes are present throughout human spinal cord, alpha1d mRNA predominates overall. If confirmed at a protein level, these findings may contribute to the development of new therapeutic strategies in the treatment of several human diseases.

Adrenoceptor involvement in the cardiovascular responses to B-HT 920 in sinoaortic denervated rats

1. A study was made relating the involvement of alpha-adrenoceptors in the cardiovascular responses to intracerebroventricular (i.c.v.) injection of B-HT 920, a clonidine-type drug, in conscious sham-operated and sinoaortic-denervated rats. 2. Wistar rats were used, 7 days after the sham operation or sinoaortic denervation. For i.c.v. injection of drugs, a guide cannula had been previously implanted in the left lateral ventricle. 3. In sham-operated rats, cardiovascular responses to B-HT 920 (10-60 microg) were increased blood pressure and bradycardia; but, in sinoaortic-denervated rats, after the pressor response, a decrease in blood pressure also was seen. The responses to this agent were greater in sinoaortic-denervated rats than in sham-operated animals. Treatment with the alpha2-adrenoceptor antagonist yohimbine (30 microg), the imidazoline receptor antagonist idazoxan (15 microg) and the alpha1A-adrenoceptor antagonist 5-methylurapidil (15 microg) blocked the responses to B-HT 920 (30 microg). The alpha1-adrenoceptor antagonist prazosin (15 microg) and the alpha1B-adrenoceptor antagonist chloroethylclonidine (100 microg) did not modify the responses to agonist. 4. Sinoaortic denervation enhances the cardiovascular responses to B-HT 920. Moreover, the effects of i.c.v. administration of B-HT 920 could be mediated by several types of brain receptors: imidazoline receptors and alpha1A- and alpha2-adrenoceptors.