Vascular smooth muscle responsiveness in a hibernator: effects of season and temperature

Abstract

To determine the effects of season, acclimation state, and hibernation on the reactivity of vascular smooth muscle from a hibernant species, strips of thoracic aorta, renal and femoral arteries, and portal vein obtained from adult woodchucks, Marmota monax, were suspended for isometric tension measurements in physiological salt solution. These blood vessels exhibited no seasonal variation in resting tension, connective tissue content, or maximum tension developed to norepinephrine. However, the concentration-response curves to norepinephrine in both aortic and portal vein strips from animals tested in May and June were shifted to the left of those from animals tested in either August or November through February. This increased sensitivity to the catecholamine was seen also in renal vessels from hibernating compared with nonhibernating animals. Decreasing organ bath temperature from 37 to 28 degrees C increased tension developed in response to norepinephrine in aortic and renal strips, whereas that of the femoral artery was unchanged. With further cooling to 17 degrees C, the responses to norepinephrine in aortic and renal strips were similar to the responses at 37 degrees C. The contraction developed to 40 mM KCl was diminished in all tissues at 28 degrees C. Blockade of beta-adrenergic receptors did not augment the response to norepinephrine at 37 degrees C. Contractions of the woodchuck aorta in calcium-free medium were sustained longer than comparable tissue obtained from a rabbit. These data suggest that receptor-mediated processes are modulated in hibernating animals. This modulation varies among vascular beds and may act to maintain or divert perfusion of the tissue through entry, during, and arousal from hibernation.

Sympathetic α-adrenergic regulation of blood flow and volume in hamsters arousing from hibernation

“…However, at low temperatures in vitro, sensitivity to adrenergic vasoconstriction is retained by vessels of hamsters (22), hedgehogs (4), ground squirrels (9), and marmots (19) and may be characteristic of all small mammalian hibernators in vivo. In hamsters (20) and sciurids (25), the induction and maintenance of thermal gradients in the body during arousal from hibernation appear to be a common strategy.…”

“…Numerous studies on isolated vessels from a variety of small mammalian hibernators have been performed, and the consensus appears to be that aortic, carotid, renal, and femoral vessels retain functional or enhanced sensitivity to adrenergic or purinergic vasoconstriction at low temperatures (4,9,19,22). In contrast, vasodilatory responses at low temperatures have been the subject of few studies.…”

Mammalian Hibernation: An Escape from the Cold

“…For example, in the euthermic woodchuck, Marmota monax (Miller et al 1986), the sensitivity to NE-stimulated tension generation in strips of the thoracic aorta and the portal vein is highest in the spring as compared to that of summer and winter, although the maximum response is constant yearround. In the hibernating state, tissue-specific differences in sensitivity to NE stimulation are evident: the renal arterial strip shows an increased sensitivity, whereas the aortic and femoral strips show no difference as compared to those observed in the warm-and cold-acclimated woodchucks.…”

Is cold acclimation of benefit to hibernating rodents?

“…Selective alteration to skeletal muscle, including disuse atrophy in the tibialis anterior muscle in golden hamsters (Mesocricetus auratus), together with preserved capillary to fibre ratio, has previously been noted (Deveci and Egginton, 2002). Control of vascular tone through adrenergic and purinergic vasoconstrictors is relatively preserved in hibernators across a range of temperatures (Eliassen and Helle, 1975;Miller et al, 1986;Saito et al, 2002). However, preliminary experiments investigating the transition between normothermia and hypothermia indicate that depressed blood pressure, heart rate (f H ) and ventilation rate (f V ) were similar when cold-acclimated (CA) and euthermic hamsters were challenged with acute cooling (Deveci and Egginton, 2007), suggesting good preservation of cardiovascular control despite hypothermic temperatures (25°C).…”