Charles S. Bockman

We evaluated an acinar cell line (SMG-C10) cloned from rat submandibular glands as a possible model for α₁-adrenoceptor regulation of submandibular function. α₁-Adrenoceptors are subdivided into three subtypes called α_1A, α_1B, and α_1D, which can be distinguished from one another by their differential affinity values for subtype-selective α₁-adrenoceptor antagonists. Thus, α₁-adrenoceptor subtypes in SMG-C10 cells were characterized with reverse transcription-polymerase chain reaction (RT-PCR) and [³H]prazosin binding in side-by-side experiments with native submandibular glands. RT-PCR identified mRNAs for α_1A-, α_1B-, and α_1D-adrenoceptors in SMG-C10 cells and submandibular glands. The inhibition of [³H]prazosin binding by 5-methylurapidil (α_1A-selective) was biphasic and fit best to a two-site binding model with 40 ± 8% high (K_iH)- and 60 ± 10% low (K_iL)-affinity binding sites in SMG-C10 cells, and 76% high- and 24% low-affinity binding sites in submandibular glands. Respective K_iH and K_iL values for 5-methylurapidil were 1.9 ± 0.4 and 100 ± 30 nM in SMG-C10 cells and 3.2 ± 0.8 and 170 ± 20 nM in submandibular glands. BMY-7378 [8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione dihydrochloride (α_1D-selective)] bound with low affinity in SMG-C10 cells and submandibular glands with K_i values of 81 ± 20 and 110 ± 20 nM, respectively. Chloroethylclondine, an irreversible alkylating agent selective for α_1B adrenoceptors, reduced the density of [³H]prazosin binding sites by 42 and 26% in SMG-C10 and submandibular membranes, respectively. Thus, SMG-C10 cells and submandibular glands are similar in expressing receptor protein for α_1A- and α_1B-adrenoceptor subtypes, establishing SMG-C10 cells as a potential model for α₁-adrenoceptor-mediated secretion.

The affinity of vascular vasopressin receptors was studied to determine its role in altered vascular contractile sensitivity in deoxycorticosterone acetate (DOCA)-salt hypertension. Ring segments of rat mesenteric arteries were used to study vascular vasopressin receptors. Male Wistar rats were given subcutaneous injections of DOCA and 1% NaCl in the drinking water. Mesenteric arteries from hypertensive rats had a reduced contractile sensitivity to arginine vasopressin (AVP) and lysine vasopressin (LVP). The order of potency of vasopressin receptor agonists (AVP greater than LVP greater than oxytocin) was the same in arteries from hypertensive compared with normotensive animals. The affinity of the vasopressin receptor antagonist [deamino-Pen1,O-Me-Tyr2,Arg8] vasopressin, and the affinities of the vasopressin receptor agonists AVP and LVP were not altered during developing DOCA-salt hypertension. There was no change in contractile sensitivity to norepinephrine and KCl in arteries from hypertensive rats. The reduced vasopressin contractile sensitivity is not due to a change in vasopressin receptor affinity but may be a compensatory response to elevated blood pressure. These data suggest that increased vascular sensitivity does not contribute to elevated blood pressure during the developing stage of DOCA-salt hypertension.