The isolated cremaster muscle preparation and (external) spermatic nerve-cremaster muscle preparation of the guinea-pig

Abstract

The isolated cremaster muscle preparation and spermatic nerve-cremaster muscle preparation of the guinea-pig were studied in vitro to determine their suitability as pharmacological test models. The preparation was contracted by acetylcholine, carbachol, succinylcholine and decamethonium (pD2 values, 4-2, 5-3, 7-3 and 7-4, respectively) through an action on a curare-sensitive cholinoceptor. Lobeline and DMPP were ineffective. Nicotine contracted the muscle, but there was tachyphylaxis. Tubocurarine and hexamethonium presumably competitively antagonized acetylcholine (pA2 values, 7-3 and 5-8); lobeline was a non-competitive antagonist (pD'2 value, 6-4). Atropine and mecamylamine exerted a dualistic action against acetylcholine (final pD'2 values, 5-3 and 6-7, respectively). Tubocurarine, succinylcholine and decamethonium exhibited their typical action when tested with spermatic nerve-cremaster muscle preparation; the latter two drugs also produced muscle spasm. Hexamethonium was a weak blocker of neuromuscular transmission. Atropine, mecamylamine, lobeline and DMPP exhibited neuromuscular blocking activity; however, directly evoked muscle twitches were also notably affected. The cremaster muscle preparations seem to add usefully to the list of currently used in vitro tests, with the added advantage that a mammalian skeletal muscle model is used for simultaneous quantitative studies.

Characterization of the Adrenoceptor in the Isolated Cremaster Muscle of the Guinea‐pig

“…There is substantial evidence that the effect of catecholamines on the slow skeletal muscle is mediated through the fl2-type of adrenoceptor (Bowman & Nott, 1970;Apperley, Daly & Levy, 1976) The directly evoked twitch responses of the guinea-pig cremaster muscle in vitro were increased by adrenaline (Kelkar, Gupta & Gokhale, 1976). In the present work an attempt is made to characterize the mechanism of this augmentation.…”

“…After displacing the testis into the abdominal cavity the cremaster was exposed as a cone shaped muscle with its apex attached to the epididymal pole of the testis, and the base fanning out towards the external abdominal ring (Kelkar et al, 1976). The whole muscle was dissected out cutting across the muscle mass at the level of the external abdominal ring.…”

“…The present experiments used the whole cremaster muscle which did not contract in response to sympathomimetic drugs. It is therefore possible that the cremaster of animals in the higher weight range, such as those used in these experiments, have very little smooth muscle especially as the response of the muscle to cholinergic drugs is blocked by tubocurarine (Kelkar et al, 1976;Dale, Evinc & Vine, 1976;Dale & Muid, 1976). Furthermore, the twitch response in the present experiments was not inhibited in the presence of verapamil, a drug which was shown to abolish selectively the evoked slow contractions in the tip of guinea-pig cremaster, originating from the smooth muscle (Ninomiya, 1975).…”

“…Catecholamines augment the tension and duration of maximal twitches of fast contracting mammalian skeletal muscle, but they have the opposite effect on slow contracting muscle (Goffart & Brown, 1947;Bowman & Zaimis, 1955;Bowman & Nott, 1969;Marsden & Meadows, 1970;Tashiro, 1973; Zaimis, 1973). There is substantial evidence that the effect of catecholamines on the slow skeletal muscle is mediated through the fl2-type of adrenoceptor (Bowman & Nott, 1970;Apperley, Daly & Levy, 1976) The directly evoked twitch responses of the guinea-pig cremaster muscle in vitro were increased by adrenaline (Kelkar, Gupta & Gokhale, 1976). In the present work an attempt is made to characterize the mechanism of this augmentation.…”

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“…Cremaster muscle was obtained from freshly killed young animals (weighing 750 g or more). After displacing the testis into the abdominal cavity the cremaster was exposed as a cone shaped muscle with its apex attached to the epididymal pole of the testis, and the base fanning out towards the external abdominal ring (Kelkar et al, 1976). The whole muscle was dissected out cutting across the muscle mass at the level of the external abdominal ring.…”