Diabetes induces sex-dependent changes in neuronal nitric oxide synthase dimerization and function in the rat gastric antrum

Abstract

Gangula PRR, Maner WL, Micci M-A, Garfield RE, Pasricha PJ. Diabetes induces sex-dependent changes in neuronal nitric oxide synthase dimerization and function in the rat gastric antrum. Am J Physiol Gastrointest Liver Physiol 292: G725-G733, 2007; doi:10.1152/ajpgi.00406.2006.-Diabetic gastroparesis is a disorder that predominantly affects women. However, the biological basis of this sex bias remains completely unknown. In this study we tested the hypothesis that a component of this effect may be mediated by the nitrergic inhibitory system of the enteric nervous system. Agematched male and female Sprague-Dawley rats were studied 8 or 12 wk after streptozotocin (55 mg/kg body wt ip)-induced sustained hyperglycemia and compared with controls. Solid gastric emptying (GE) studies were performed in all the groups. Changes in gastric antrum neuronal nitric oxide synthase (nNOS) mRNA and protein levels were analyzed by real-time PCR and Western immunoblotting, respectively. nNOS dimerization studies were performed using lowtemperature SDS-PAGE. In vitro nitrergic relaxation (area under curve/mg tissue wt) was studied after the application of electric field stimulation in an organ bath. Changes in intragastric pressure (mmHg⅐s) in freely moving rats in the presence or absence of N Gnitro-L-arginine methyl ester (nitric oxide synthase inhibitor) were examined by an ambulatory telemetric method. After diabetes induction, GE is delayed in both male and female rats. However, diabetic females exhibited significant delayed GE than in diabetic males. Compared with male controls, gastric nNOS expression and nitrergic relaxation were substantially elevated in healthy female control rats, accompanied by significantly reduced intragastric pressure. The active dimeric form and dimer-to-monomer ratio of nNOS␣ were also higher in healthy females compared with male rats (P Ͻ 0.05). Diabetic females, but not males, showed significant (P Ͻ 0.05) impairment in both gastric nNOS␣ dimerization and nitrergic relaxation, accompanied by an increase in intragastric pressure. Our data provide evidence that females may have a greater dependency on the nitrergic mechanisms in health. Furthermore, diabetes seems to affect the nitrergic system to a greater extent in females than in males. Together, these changes may account for the greater vulnerability of females to diabetic gastric dysfunction.solid gastric emptying; nitrergic relaxation; intragastric pressure GASTRIC DYSMOTILITY OR GASTROPATHY occurs in 20 -55% of patients with Type 1 (insulin dependent) and up to 30% of patients with Type 2 diabetes (non-insulin dependent) (37). Symptoms of diabetic gastropathy can range from mild dyspepsia to recurrent vomiting and abdominal pain and are often associated with delayed or accelerated gastric emptying. Fundic tone abnormalities and/or poor antroduodenal coordination has been reported in diabetic patients (28). Although the pathogenesis of diabetic gastropathy is not completely understood, it appears to be much more common (up to four times) in w...

Tetrahydrobiopterin (BH4), a cofactor for nNOS, restores gastric emptying and nNOS expression in female diabetic rats

“…There is a striking sex bias in gastroparetic patients, with women outnumbering men by a 4:1 ratio (18,19,34). Recent findings from our laboratory demonstrate that the reduction in gastric emptying is greater in female rats compared with males after diabetes induction (14). In addition, the study suggested that at least one biological reason for this sex bias may be differences in nitrergic regulation of gastric motility, with females being more vulnerable to changes in this system (14).…”

“…At the end of 3-wk BH4 supplementation, solid gastric emptying studies were performed as described previously (14). The rate of gastric emptying was calculated according to the following equation: gastric emptying (% in 4 h) ϭ (1 Ϫ gastric content/food intake) ϫ 100.…”

“…Ambulatory telemetric studies. Gastric contractility was measured using an ambulatory telemetric apparatus as described in our previous study (14). Each animal was implanted with a pressure transducer in gastric lumen 1 wk before experiment.…”

“…Recent findings from our laboratory demonstrate that the reduction in gastric emptying is greater in female rats compared with males after diabetes induction (14). In addition, the study suggested that at least one biological reason for this sex bias may be differences in nitrergic regulation of gastric motility, with females being more vulnerable to changes in this system (14). Therefore, in the present study, we sought to examine the mechanisms underlying such changes.…”

Diabetic gastroparesis - from diagnosis to gastric electrical stimulation treatment

“…One explanation is the fact that gastric emptying in female gender is on average slower than in males 12 . The other possible explanation is based on recent animal data which pointed that the effect of diabetes mellitus on the enteric nervous system is more expressed in females 14,15 .…”