Short-term administration of growth hormone (GH) lowers blood pressure by activating eNOS/nitric oxide (NO)-pathway in male hypophysectomized (Hx) rats

• BACKGROUND: The aim of the study was to evaluate the acute and continuous (up to 14 days of treatment) effect of growth hormone (GH) on blood pressure (BP) regulation and to investigate the interplay between GH, nitric oxide (NO) and BP. In un-supplemented and GH supplemented hypophysectomized (Hx) male rats as well as intact rats, continuous resting mean arterial blood pressure (MAP) was measured using telemetry. Baroreceptor activity and the influences of NO on BP control were assessed during telemetric measurement. Furthermore, basal plasma and urine nitrate levels and aortic endothelial nitric oxide synthase (eNOS) expression were analysed. Endothelial function as well as vascular structure in the hindquarter vascular bed was estimated using an in vivo constant-flow preparation. RESULTS: Hypophysectomy was associated with decreased MAP (Hx: 83 +/- 3 vs Intact: 98 +/- 6 mmHg, p < 0.05) and heart rate (HR) (Hx: 291 +/- 4 vs Intact: 351 +/- 7 beat/min, p < 0.05). Endothelial dysfunction and reduced vasculature mass in the hindquarter vascular bed was found in Hx rats. GH substitution caused a further transient decrease in MAP and a transient increase in HR (14% and 16% respectively, p < 0.05). The reduction in MAP appeared to be NO dependent. Aortic eNOS expression was unchanged. GH substitution resulted in an impaired baroreceptor function. Two weeks of GH treatment did not normalise the BP, vascular structure and the endothelial function in the resistance vessels. CONCLUSION: GH substitution seems to have a short lasting effect on lowering blood pressure via activation of the NO-system. An interaction between GH, NO-system and BP regulation can be demonstrated.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  (hsv//swe)

MEDICAL AND HEALTH SCIENCES  (hsv//eng)

Nyckelord

MEDICIN

MEDICINE

Animals

Blood Pressure/*drug effects/physiology

Blood Vessels/drug effects/physiology

Body Weight/drug effects

Drug Administration Schedule

Enzyme Activation/drug effects

Enzyme Inhibitors/pharmacology

Growth Hormone/*administration & dosage/pharmacology

Heart/anatomy & histology

Heart Rate/drug effects

*Hypophysectomy

Insulin-Like Growth Factor I/metabolism

Male

Muscle

Skeletal/blood supply

NG-Nitroarginine Methyl Ester/pharmacology

Nitrates/blood/urine

Nitric Oxide/*metabolism

Nitric Oxide Synthase Type III/*metabolism

Organ Size/drug effects

Pressoreceptors/drug effects

Rats

Rats

Wistar

Vascular Resistance

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