Loss of nocturnal dipping of blood pressure and heart rate in obesity-induced hypertension in rabbits

We have investigated in rabbits whether overfeeding and weight gain, which lead to hypertension, are associated with changes in circadian rhythm of bl ood pressure (BP) and heart rate, and whether the sympathetic nervous syste m is involved in these changes. In adult male rabbits, mean arterial pressure (MAP) and heart rate (HR) wer e monitored by telemetry 22 h a day. Daily MAP and HR records were divided into four equal intervals and used to calculate day-night differences. Afte r a 1-week control period, animals were switched to a high-fee (HFD) ad lib itum diet for 8 weeks. HFD increased whole day MAP and KR, and rapidly abol ished the normal diurnal rhythm of MAP and HR. Since HFD abolished the noct urnal dip in MAP, but had little effect on daytime values, the loss of dipp ing appears to account for most of the hypertension in this model of obesit y. In a separate set of rabbits, alpha- and beta -adrenergic blockade (terazos in + propranolol) prevented HFD-induced hypertension and attenuated the inc rease in HR by more than half. Adrenergic blockade alone abolished the diur nal rhythm of MAP, chiefly by preventing daytime elevation of MAP. The addi tion of HFD ad libitum did not further modify daily MAP or its circadian pa ttern. The diurnal rhythm of RR was relatively unaffected by alpha + beta b lockade alone, but was abolished after switching to HFD. In conclusion, rabbits fed an HFD ad libitum develop hypertension and tachy cardia associated with a loss of the normal diurnal rhythm of MAP and HR. T he hypertension appears to be sympathetically mediated. (C) 2001 Elsevier S cience B.V. All rights reserved.