Release of contractile agents from rat vas deferens by clonidine

Functionomics: the analysis of a postgenomic concept on the basis of pregenomic pharmacological studies in smooth muscle

The term functionomics (Amin 2003, Neumann et al. 2004) refers to a postgenomic integrated Systems Biology (Attur et al. 2002) using a multidimensional approach for cells, tissues and organs. It considers current or future involvement among genomics, proteomics or metabolomics, including the main factors that cause biological responses and modulation under different conditions. Our objective in the present review is to summarize the contemporary understanding of functionomics of smooth muscle pharmacology, based on the results obtained on the pregenomic era during several years in our laboratory. The present approach is based on the knowledge of the dynamics of the receptor system, which comprises a cascade of phenomena, leading from the drug administration to the final biological response. We will describe several conditions in which the final effect is modified, based on perturbations induced on drug absorption, distribution, metabolism, interaction with receptors and mobilization of second messengers, as well as by interactions with a second receptor system. We will also discuss the gaps that need to be fulfilled in order to obtain a clear and better understanding of the receptor system in smooth muscle, and to narrow the bridge between ourknowledge of the function of biological systems, genomics, and other recently introduced areas.

Mechanisms of adaptive supersensitivity in vas deferens

Adaptive supersensitivity is a phenomenon characteristic of excitable tissues and discloses as a compensatory adjustment of tissue's response to unrelated stimulatory endogenous and exogenous substances after chronic interruption of excitatory neurotransmission. The mechanisms underlying such higher postjunctional sensitivity have been postulated for a variety of cell types. In smooth muscles, especially the vas deferens with its rich sympathetic innervation, the mechanisms responsible for supersensitivity are partly understood and appear to be different from one species to another. The present review provides a general understanding of adaptive supersensitivity and emphasizes early and recent information about the putative mechanisms involved in this phenomenon in rodent vas deferens.

Contractile responses of the rat vas deferens after epithelium removal

The purpose of the present investigation was to verify the role of the epithelium in the functional response of the rat vas deferens. Our results showed that the contractile effect of cumulative doses of clonidine (3.10(-5)-3.10(-3)) was increased after the removal of the epithelium. The effect of clonidine in epithelium-free vas deferens returned to normal values when an isolated epithelium from another vas deferens was added to the organ bath, showing that the epithelium is responsible for this increase of maximum effect for clonidine. Drugs functionally or structurally related to clonidine, such as oxymetazoline, alpha-methylnorepinephrine and moxonidine, did not have their dose-response curves altered. The curves for other contractile agents, such as noradrenaline, acetylcholine, ATP, 5HT, bradykinin and histamine, or the relaxation induced by isoprenaline and forskolin were also not modified. Electrically-induced contractions at frequencies from 0.1 to 20 Hz and the mechanism of negative feed-back, brought about by clonidine (10(-10)-10(-8) M) through pre-synaptic alpha2-adrenoceptors, were not changed after the removal of epithelium. In conclusion, a significant function of the epithelium in the contractility of the rat vas deferens was demonstrated for clonidine, but not for other agonists.

Functional properties of agmatine in rat vas deferens

Experiments were performed with rat vas deferens to verify whether agmatine, an endogenous ligand for adrenoceptors and imidazoline receptors, can influence sympathetic neurotransmission, with respect to contractions induced by transmural nerve stimulation, contractions induced by exogenous noradrenaline, and overflow of endogenous noradrenaline. It was shown that agmatine (a) caused a dose-dependent potentiation of electrically induced twitches, up to about 70% in relation to controls, (b) shifted to the right the inhibitory concentration-response curves for clonidine on electrically induced twitches, indicating competitive antagonism at presynaptic alpha-adrenoceptors, with a pA2 value of 4.12 +/- 0.10, (c) shifted to the right the concentration-response curves for noradrenaline-induced contractions, indicating competitive antagonism at postsynaptic alpha-adrenoceptors as well, with a pA2 value of 4.03 +/- 0.10, and (d) caused a dose-dependent increase of KCI-induced overflow of noradrenaline, up to about 90% in relation to controls. It is concluded that agmatine has multiple effects on sympathetic neurotransmission in rat vas deferens.

Evidence for participation of nitric oxide in excitatory neurotransmission in rat vas deferens

A depression of the fast, non-adrenergic, and also of the slow, adrenergic, components of muscle contraction in response to intramural nerve stimulation was induced by the blocker of nitric oxide synthase NG-nitro-L-arginine methyl ester (L-NAME), in rat vas deferens. Effects of exogenous noradrenaline or ATP were not reduced by L-NAME. However, L-arginine also caused an inhibition of electrically induced effects in most of the preparations, contrary to the expectations for a precursor of nitric oxide synthesis. In spite of these difficulties L-arginine antagonized the action of L-NAME. These results indicate that nitric oxide is involved in excitatory nerve-muscle transmission in vas deferens.