Some Pharmacological Properties of the Cremaster Muscle of the Guinea‐pig

Abstract

I The tension developed in the guinea-pig cremaster was recorded during spontaneous activity and electrical stimulation. Spontaneous rhythmic contraction was observed in many preparations, particularly in the tip of the cremaster. These contractions were very slow, lasting about 20 s and occurring at about 2 min intervals, but different preparations varied greatly. Twitches produced by electrical stimulation were similar to those in other skeletal muscles, being reduced by (+)-tubocurarine and abolished by tetrodotoxin. 2 A slow contraction could be initiated by electrical stimulation using a pulse longer than 10 ms in spontaneously active preparations and in some quiescent preparations. Spontaneous and evoked slow contractions were not suppressed by tetrodotoxin, but were selectively abolished by verapamil. Histamine increased the basal tension and generated spontaneous contractions in quiescent preparations. Hypertonic solutions also had excitatory effects. 3 Contractions produced by acetylcholine and carbachol were blocked by atropine. Those produced by adrenaline and noradrenaline were stronger than those due to histamine, acetylcholine and carbachol and were abolished by an ax-adrenoceptor blocking agent, phentolamine. In the preparations in which the slow contraction was not observed, histamine, acetylcholine or adrenaline had very little effect. 4 It is suggested that the cremaster muscle consists of striated muscle together with some smooth muscle having properties similar to that in the vas deferens.

Morphological Studies of Fiber Types of Striated Muscle Fibers of the Cremaster in the Guinea Pig

“…This conclusion is consistent with the phar macological properties of this muscle [Ninomiya, 1975;Dale and Muid, 1976],…”

“…Although we have no satisfactory explana tion for this difference, such could be tentatively attributed to the shortness of the fibers isolated from the cremaster muscle. The above interpretation regarding the nature of the two types of muscle fibers found in the cremaster muscle is consistent with the results of the pharmacological studies referred to in the introduction [Ninomiya, 1975;Dale and Muid, 1976]. In fact, since it is well known that twitch fibers display sodium-dependent action potentials [Chiarandini and Stefani, 1979], the finding that tetrodotoxin [a selective blocking agent of the sodium channels; Kao, 1966] abolishes the twitch elicited by electrical stimulation of the isolated cremaster muscle, suggests that the mechanical response origi nates mainly in fibers of the twitch type; this latter assumption is consistent with the pre sent observation suggesting that slow muscle fibers are rather scarce in the cremaster muscle of the guinea pig.…”

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

“…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). We assume therefore, that the twitch response to direct electrical stimulation in the present work was due to a contraction of skeletal muscle.…”

“…Higher concentrations of (+) -INPEA or isoxsuprine (Table 1) markedly inhibited the twitch response; while isox5uprine now afforded a considerable protection against isoprenaline, the protective effect of (+) -INPEA was no better than that of the lower concentration of this drug. (Ninomiya, 1975). The present experiments used the whole cremaster muscle which did not contract in response to sympathomimetic drugs.…”

Structural Alterations and Changes in the Distribution of Markers in Transected Skeletal Muscle Fibers of the Guinea Pig

“…In special conditions, however, the skeletal muscle fi bers of the frog sartorius with a small lesion (2-4 pm), when bathed with isotonic cal cium solution, heals over in a few milli seconds, while larger injuries do not heal over [De Mello, 1972], A transection of the rat diaphragm is followed by a membrane potential (MP) drop from -75 to -15 mV after 1-2 h [Barstad, 1962], suggesting that this muscle lacks healing-over ability. In contrast to this, the striated muscle of guinea pig cremaster maintains its electrical [ Alonso- de Florida et al, 1972], mechanical and pharmacological properties [Ninomiya, 1975] after the transection of its fibers. Moreover, measuring the change of MP after the transverse severance of striated fib ers of cremaster muscle, a depolarization reaching a peak value a few minutes after the lesion was found.…”