Summary
Fifteen days after duct ligation, the wet weight of the rat submaxillary gland was reduced to 40% of the contralateral control. Under these experimental conditions, the noradrenaline (NA) content expressed as μg/g was 1.2±0.1 in the control glands and 1.9±0.2 in the atrophied glands.
The accumulation of 3H-NA in the tissue expressed as μCi/gland, did not differ when the atrophied glands were compared with the corresponding controls. Consequently, the uptake and retention of 3H-NA was not modified by the atrophy of the secretory cells of the gland.
The spontaneous efflux of radioactivity from normal and atrophied submaxillary glands prelabelled with 3H-NA was similar. The analysis of the metabolic pattern in both experimental groups revealed that in the spontaneous outflow and also during potassium-induced depolarization, the formation of the O-methylated metabolite, 3H-normetanephrine (NMN) was reduced by more than 50% in the atrophied glands. During depolarization induced by K+, a 2-fold increase in the outflow of the deaminated glycol 3H-3,4-dihydroxyphenylglycol (DOPEG) was observed.
The effect of phentolamine on the release of radioactivity induced by 60 mM K+ in normal and in atrophied submaxillary gland slices prelabelled with 3H-NA was also investigated. In both experimental groups, the fractional release of total radioactivity induced by K+ was similar. Phentolamine, 3.1 μM, produced a 3-fold increase in the fractional release of radioactivity both in the control and the atrophied glands. These results indicate that the increase of K+-induced release of 3H-NA induced by phentolamine was independent of the presence or absence of the postsynaptic structures. It is concluded that phentolamine increases transmitter release by blocking alpha-adrenoceptors located in the noradrenergic nerve endings of the rat submaxillary gland.
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Filinger, E.J., Langer, S.Z., Perec, C.J. et al. Evidence for the presynaptic location of the alpha-adrenoceptors which regulate noradrenaline release in the rat submaxillary gland. Naunyn-Schmiedeberg's Arch. Pharmacol. 304, 21–26 (1978). https://doi.org/10.1007/BF00501373
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DOI: https://doi.org/10.1007/BF00501373