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1682043 
Journal Article 
Pharmacology and thermosensitivity of the dartos muscle isolated from rat scrotum 
Gibson, A; Akinrinsola, A; Patel, T; Ray, A; Tucker, J; Mcfadzean, I 
2002 
Yes 
British Journal of Pharmacology
ISSN: 0007-1188
EISSN: 1476-5381 
136 
8 
1194-1200 
12163353 
WOS:000177471600017 
1 The dartos is a thin sheet of smooth muscle closely associated with the skin of the scrotum. Although known to play an important role in scrotal thermoregulation, there has been no detailed study into the pharmacology, or thermosensitivity, of the dartos from any species. Here, we investigate these two parameters in the isolated dartos muscle from rat.



2 Field stimulation of the rat dartos caused contractions that were abolished by tetrodotoxin, phentolamine and guanethidine, but unaffected by atropine or L-N(G)-nitroarginine. Exogenous noradrenaline also produced contractions blocked by both phentolamine and prazosin. In muscles with raised tone and negated sympathetic function, field stimulation failed to elicit relaxation. The dartos muscle did not contract in response to carbachol, nicotine, histamine, 5-hydroxytryptamine (all up to 100 pm) or substance P (up to 1 muM.



3 Contractile responses to field stimulation and noradrenaline were much greater at 30degreesC compared with 40degreesC; indeed, contractions to 1 muM noradrenalme at 30degreesC were relaxed by around 80% on heating to 40degreesC. Similar heat-induced relaxations were observed during contractions to both U46619 (100 nM) and high K (70 mm).



4 In contrast, contractile responses to the myosin phosphatase inhibitor calyculin-A (1 muM), either in the presence or absence of external calcium, were resistant to relaxation by heating. In calcium-free medium at 30degreesC, U46619 continued to produce contractions that were again relaxed by 80% on heating to 40degreesC. However, in the presence of calyculin-A, this heat-induced relaxation was greatly reduced.



5 Thus, the rat dartos muscle receives a functional sympathetic innervation and contracts to noradrenaline via alpha-adrenoceptors. There is no functional inhibitory innervation. Experiments with calyculin-A suggest that myosin phosphatase is a major contributor to the marked thermosensitivity of the dartos muscle. 
calyculin-A; dartos (rat); myosin phosphatase; noradrenaline; scrotum; sympathetic; temperature; U46619