Alpha1 and alpha2 adrenoceptor mediated melanosome aggregatory responses in vitro in Oreochromis mossambica (Peters) melanophores.

Effects of specific and non-specific adrenoceptor agonists and antagonists were examined on the isolated scale melanophores of O. mossambica in physiological Ringer solution. The responses were recorded as melanophore size index. It was observed that adrenaline, nor-adrenaline, phenylpropanolamine, clonidine and phenylepherine induced melanosome aggregation in a dose-dependent manner. Denervation of the fish melanophores increased the sensitivity of the melanophores to adrenaline but not to nor-adrenaline. Phentolamine (3.55 x 10(-5) M), prazosin (2.38 x 10(-5) M) and yohimbine (2.821 x 10(-5) M) significantly inhibited the aggregatory responses of the fish melanophores to adrenaline, nor-adrenaline, clonidine and phenylepherine. The blocking effect of yohimbine was significantly higher than that of prazosin. It is concluded that the effect of adrenaline is directly mediated through the receptors and alpha2 adrenoceptors are predominantly involved in the aggregatory responses of this fish melanophores, while alpha1 adrenoceptors presence has been indicated.

CNS alpha 1 receptor in tonic pain during estrous cycle in rats.

Estrogen and progesterone are known to affect nociception. The plasma concentrations of these hormones vary during estrous cycle in rodents. The aim of the present study was to investigate the effect of evidence of alpha1 receptor agonist and antagonist on tonic pain in all phases of estrous cycle in female rats. Phenylephrine (alpha1 agonist) and prazosin (alpha1 antagonist) were administered via intracerebroventicular (ICV) injection. Adult female rats weighting 200-220 g were maintained on 12 h light/dark cycle for 10-14 days prior to the experiment. Food and water were made available ad libitum. Formalin test was performed in all phases of estrous cycle. Results showed that phenylephrine caused significant (P<0.05) reduction in pain sensitivity. This reduction was more pronounced during proestrus phase. Prazosin significantly (P<0.05) increased pain sensitivity, particularly during metestrus phase. It is possible that fluctuation in pain sensitivity during estrous cycle is related to the level of sex hormones during estrous cycle.

Comparison of relaxation responses of cavernous and trigonal smooth muscles from rabbits by alpha1-adrenoceptor antagonists; prazosin, terazosin, doxazosin, and tamsulosin

Alpha1a-adrenergic receptor (AR) primarily mediates the contraction of the prostatic and cavernous smooth muscles. Among clinically available alpha1-AR antagonists for the medical management of benign prostatic hyperplasia (BPH), tamsulosin has a modest selectivity for alpha1A- and alpha1D- over alpha1B-ARs. To compare the effects of various alpha1-AR antagonists on relaxation responses of cavernous and trigonal smooth muscles, isometric tension studies with relatively selective (tamsulosin) and non-selective (prazosin, doxazosin, and terazosin) alpha1A-AR antagonists, were conducted in the cavernous and trigonal muscle strips of rabbits (n=10 each). Tamsulosin had the strongest inhibitory effect on contraction of trigonal smooth muscle among the various alpha1-AR antagonists, and the inhibitory activities of prazosin, doxazosin, and terazosin were not statistically different. All alpha1-AR antagonists caused concentration-dependent relaxation of the cavernous muscle strips. Tamsulosin was shown to have greater potency than prazosin (more than 100-fold), doxazosin (more than 1000-fold), and terazosin (more than 1000-fold), in relaxation of cavernous smooth muscle. In conclusion, tamsulosin might be the most effective drug among the four commonly used alpha1-AR antagonists for the medical management of BPH. Tamsulosin might be a potential substitute for phentolamine in combination with vasoactive agents as an intracavernous injection therapy for patients with erectile dysfunction.