Abstract
Previous studies from this laboratory have demonstrated an enhancement in both the contractile and signaling response to stimulation of eitheralpha-1 adrenoceptors or guanine nucleotide binding proteins (G proteins) in arteries from male Wistar rats with 12 to 14 weeks of streptozotocin-induced diabetes. The purpose of the present investigation was to determine whether changes in arterialalpha-1 adrenoceptors or the G proteins coupled to them are associated with the enhanced responsiveness of the diabetic arteries. No difference in affinity was detected between control and diabetic aorta or caudal artery membranes in saturation binding of [3H]prazosin to alpha-1 adrenoceptors. However, the alpha-1 adrenoceptor number was significantly decreased in caudal artery but not aorta from diabetic rats. In competition binding experiments, a low-affinity and a high-affinity binding site for norepinephrine were detected in the absence of guanine nucleotides and NaCl in control arteries, whereas only the low-affinity site was detected in diabetic arteries, suggesting that coupling of the alpha-1 adrenoceptor to G proteins is impaired in diabetic aorta and caudal artery. The levels of immunoreactive Gi2,3α and Gq/11α were not different between control and diabetic aorta or caudal artery. Thus, not only do changes in the number and coupling of thealpha-1 adrenoceptor or level of G proteins not explain the enhanced contractile responses of diabetic arteries to norepinephrine, but also the changes in alpha-1 adrenoceptor binding would counteract the enhancement. Instead, an increase in the activity of the G proteins or phospholipase C-β coupled to the alpha-1 adrenoceptor may be mediating the enhanced responsiveness elicited by alpha-1 adrenoceptor stimulation in diabetic arteries.
Footnotes
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Send reprint requests to: Dr. Kathleen M. MacLeod, Faculty of Pharmaceutical Sciences, University of British Columbia, 2146 East Mall, U.B.C., Vancouver, B.C., Canada, V6T 1Z3.
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↵1 This work was supported by the Heart and Stroke Foundation of B.C. and Yukon. L.W. is the recipient of a research traineeship from the Heart and Stroke Foundation of Canada.
- Abbreviations:
- ANOVA
- analysis of variance
- DAG
- diacylglycerol
- ECL
- enhanced chemiluminescence
- EGTA
- ethyleneglycol-bis-(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid
- Gpp(NH)p
- guanosine-5′-(β,γ-imido)triphosphate
- G protein
- guanine nucleotide binding protein
- Ins(1
- 4,5)P3, inositol-1,4,5-trisphosphate
- NA
- norepinephrine
- PIP2
- phosphatidyl inositol-4,5-bisphosphate
- PLC
- phospholipase C
- PNS
- postnuclear supernatant
- PTX
- pertussis toxin
- STZ
- streptozotocin
- Received December 13, 1997.
- Accepted August 28, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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