Vascular Dilatatory Responses to Sodium Nitroprusside (SNP) and α-Adrenergic Antagonism in Female and Male Normal and Diabetic Rats (44433)

Abstract

Diabetes Is associated with impaired vascular dllatatory responses that appear to be Influenced by sex as well as diabetic state. Therefore, we hypothesized that vascular and sympathetic control function exhibit a greater deterioration following the Induction of diabetes in female than In male rats. We conducted a comparative determination of the effect of sodium nitroprusside (SNP,a nitrous oxide donor) and that of an a1-adrenerglc antagonist, prazosln, on selective vascular flows, mean arterial pressure (MAP), and heart rate (HR), in female and male normal and diabetic rats. Rats were made diabetic using streptozotocln (50 mglkg, iv) and maintained for 5-6 weeks. Following anesthesia with urethane/a-chloralose, the femoral artery and vein were cannulated for recording and sampling. Flow probes were placed on the iliac, renal, and superior mesenteric arteries. SNP (1, 5, 10, and 20 IJglkg) Infusions resulted In a dose-dependent decrease in MAP in normal and diabetic rats. The decrease In MAP In normal males was 37% less at the 20 IJglkg concentration of SNP when compared to normal females. The HR was not significantly changed in response to the hypotensive effect of SNP; however, reflex tachycardia was more prominent in diabetic males. The vascular conductance (flow/MAP) was Increased by SNP in normal and diabetic rats in a dose-dependent fashion; however, the responsiveness was decreased in the iliac and superior mesenteric and increased in the renal arteries in diabetics when compared to normals. Diabetic males were 42%and 28% less responsive to SNP in the iliac and superior mesenteric arteries, respectively. On the other hand, diabetic females were 1.S-fold more responsive in the renal artery when compared to normals. Prazosin (4 mgikg) decreased the MAP in normal and diabetic rats to a comparable degree. Prazosin Increased the vascular conductance in all three vascular beds in normal and diabetic rats with the greater increase occurring in the Iliac (118%) and superior mesenteric (110%) arteries. We concluded that diabetes is associated with an increased response to NO In the renal vesseis and a decreased response in the iliac and superior mesenteric vessels in both females and males. a-Adrenergic tone was greatest In diabetic female and male rats. This stUdy suggests that decreased vascular flow in diabetes Is a result of a combination of decreased sensitivity to NO and increased adrenergic tone. [P.S.E.B.M. 1999, Vol 222] Funding for this research was received from grants NIH GM-08167 and NIMH 47181. I To whom requests for reprints should be addressed at Department of Physiology. Wayne State University School of Medicine, 5374 Scott Hall, 540 E. Canfield, Detroit, MI 48201. E-mail: jdunbar@med.wayne.edu Received October 2. 1998. [P.S.E.B.M. 1999. Vol 222] Accepted June I7. 1999. 0037-9727/99/2221-0090$14.00/0 Copyright © 1999 by the Society for Experimental Biology and Medicine Amajor complication of diabetes mellitus is vascular disease that leads to altered peripheral blood flow at the microand macrovascular levels, artherosclerosis, hypertension, retinopathy, and chronic ulceration (1-6). Since circulation abnormalities have been implicated in diabetic complications, investigations have focused on the role of the endothelium in the regulation of vascular tone (7). Diabetes is primarily associated with impaired vascular dilatory responses, and these responses appear to be influenced by sex as well as the diabetic state (1-6). Conse90 SEX, DIABETES, AND CARDIOVASCULAR RESPONSES quently, we propose that vascular and sympathetic control function exhibit a greater deterioration following the induction of diabetes in female than in male rats. The endothelium production of nitric oxide (NO), a potent vasodilator, plays a regulatory role in the maintenance of blood pressure and the regulation of resting vascular tone in different vascular beds (8-11). NO agonists and antagonists have been useful in characterizing the functional role of NO in regulation of mean arterial pressure (MAP), control of peripheral vascular tone, and endothelial dysfunction in diabetes (11-13). In addition to the decreased NO production associated with diabetes, endothelial NO-mediated vasodilation may also be impaired in diabetes (14). It has been suggested that this endothelial dysfunction or reduced response to endothelial NO in diabetes contributes to the development of diabetic vascular diseases (8, 14). The first goal of this study was to examine the effect of sex and diabetes on smooth muscle sensitivity to NO as modulated by the administration of SNP, a nitrous oxide donor, in normal and diabetic female and male rats. Investigations by our laboratories and others have suggested alterations in sympathetic-mediated vascular tone as a cause of diabetic vascular disease (6, 15-17). The enhanced vessel reactivity, especially of the resistance vessels to a specific agonist has been demonstrated (3, 6). Both in vitro and in vivo studies have demonstrated an increased sensitivity especially to an adrenergic agonist in animals with experimental diabetes and to control levels of circulating catecholamines (11, 18, 19). Consequently, the second goal of this study was to evaluate comparatively the effect of sex and/or diabetes on basal and regional adrenergic tone following the administration of an aI-adrenergic antagonist. Materials and Methods Normal and diabetic female and male, Wistar rats (BW: 250-275 g) were used in our experimental procedures. They were kept in a controlled environment with a 12-hr light cycle and a 23°C room temperature with free access to water and food. Diabetes was induced in normal rats by a single intravenous tail vein injection of 50 mg/kg streptozotocin (STZ) dissolved in sodium citrate (0.1 roM, pH 4.5). Five days after the STZ injection, a blood sample was collected to determine hyperglycemia, which was maintained 4-6 weeks post-STZ injection. On the day of the study and following a 24-hr fast, normal or diabetic rats were anesthetized with urethane (0.5 mglkg) and a-chloralose (70 mglkg) and placed on a heating pad to maintain their body temperature. A tracheotomy was performed to diminish respiratory obstructions, and catheters with heparinized saline were placed into the femoral artery and veins. The venous catheter was used for blood sample collection and infusions. The femoral artery cannula was used for cardiovascular recording. Pulsed-Doppler blood flow transducers (flow probe, Baylor Electronics, Houston, TX) were placed around the iliac, renal, and superior mesenteric arteries. The arterial catheter was connected to a pressure transducer, and the flow probes were connected to a pulsed-Doppler flowmeter (Baylor Electronics). Female and male normal and diabetic rats were given subsequent bolus injections of increasing concentrations of sodium nitroprusside (SNP; I, 5, 10, and 20 !J..g/kg) in 20min intervals following the establishment of a baseline. On the other hand, prazosin (4 mg/kg) was administered as a single bolus injection 10 min after the establishment of a baseline. Mean arterial pressure (MAP), heart rate (HR), and blood flow (iliac, renal, and superior mesenteric) were monitored continuously. The Biowindows software program (Modular Instruments, Malvern, PA) and a Micro 5000 signal processing system were used to monitor cardiovascular responses. The Biowindows program records all cardiovascular parameters: mean arterial pressure (MAP), heart rate (HR), and blood flow (Hz Ds units). Blood samples, 0.2 ml with saline replacement, were collected prior to the study and used for glucose analysis (glucose analyzer; Yellow Springs Instruments Co., Yellow Springs, OH). The SNP data presented are peak responses following treatments. Prazosin data are averages of l-min intervals for the reported periods post-treatment. The data were analyzed using two-way ANOV A, post hoc analysis where appropriate, and Student's t test. All studies involving the use of animals were conducted in compliance with applicable laws and regulations as well as the principles expressed in the National Institutes of Health, USPHS, Guide for the Care and Use of Laboratory Animals, and the studies were conducted on animals that were lawfully acquired. Use of animals was approved by the Wayne State University Animal Care and Use Committee. Results The body weight was decreased in females diabetics, and the blood glucose was increased in female and male diabetics when compared to normals. No significant differences were seen in basal MAP between groups. However, diabetic males had a significantly lower basal HR when compared with their corresponding counterpart (Table I). The administration of SNP resulted in a rapid decrease in MAP in normal and diabetic animals in a dose-dependent fashion (Figs. IA and 2A). Normal males tended to have less of a decrease in MAP with increasing concentrations of SNP when compared to normal females. However, this response was significant only at the 20 ug/kg concentration of SNP (Table II). The HR was increased in normal and diabetic animals (Fig. IB). All four groups of animals demonstrated a reflexive increase in HR (Figs. 1B and 2B) following SNP treatments. Normal animals tended to have greater increases in HR when compared to diabetic animals and diabetic males had a significantly smaller increase in HR when compared to diabetic females at the lower concentration of SNP, I !J..glkg (Table II). SEX, DIABETES, AND CARDIOVASCULAR RESPONSES 91 Table I. Basal Body Weight, Blood Glucose, Mean Arterial Pressure, and Heart Rate in SNPand Prazosin-Treated Normal and Diabetic Rats