Effects of dopamine on the secretion of glycoproteins from the functional segments of the rat submandibular gland.

The action of dopamine (DA) on salivation and the secretion of marker glycoproteins (GP) from secretory cells of the rat submandibular gland (SMG) was investigated using various blockers at doses of 1 or 2 mg/kg (i.v.). DA at doses from 5 to 40 mg/kg (i.p.) dose-dependently increased salivation and the concentration of protein in SMG saliva. The order of inhibitory potency on salivation was propranolol (PPR) greater than phentolamine (PHN) much greater than haloperidol (HAL) when DA was administered i.p. at a dose of 10 mg/kg and PHN much greater than HAL much greater than PPR when the dose of DA was 40 mg/kg. The concentration of protein in saliva after pretreatment with HAL or PHN increased significantly at a dose of 40 mg/kg of DA, but did not increase at a dose of 10 mg/kg of DA. Moreover, pretreatment with PPR decreased it at both doses of DA. The electrophoretic profiles of GP in DA-evoked saliva showed two characteristic main bands of GP I (130 KDa) and GP IV (21.5 KDa) contained in the acinar cells (AC) and a minor band of GP III (31 KDa) which originated from the granular tubular cells (GT). The profile was not changed by pretreatment with PHN and HAL when DA was administered at a dose of 10 mg/kg, but at a dose of 40 mg/kg, the intensity of band I increased. Pretreatment with PPR, when DA was administered at 40 mg/kg, caused an increase in the intensity of band III and a reduction in that of band I. These results suggest that DA, at low doses, affects the AC, whereas at a higher dose, it affects both the AC and GT.