Cyclic nucleotide levels in brains of control and hypertensive rats

Cyclic AMP generation in medulla oblongata and hypothalamus of hypertension-prone and -resistant rats

Accumulation of cAMP induced by noradrenaline (NA) was higher in the medulla oblongata (MO) of hypertension-prone (H) than in resistant (N) rats, 113 +/- 3 vs. 72 +/- 4 (p less than 0.01). In the hypothalamus (HYP) it was higher in N than in H rats, 148 +/- 8 vs. 92 +/- 6 (p less than 0.01). In both anterior and posterior HYP, the accumulation of cAMP was significantly higher in N than in H rats. cAMP accumulation, in the presence of increasing concentrations of phosphodiesterase inhibitor, showed significant strain differences in both MO and HYP. The observed strain differences in cAMP may be pertinent to the disparate susceptibility to hypertension of H and N rats.

Thermoregulation in spontaneously hypertensive rats: effects of antihypertensive treatments

Colonic temperature was measured in spontaneously hypertensive (SHR), Wistar Kyoto (WKY) and Wistar Charles River (WIS) rats. The SHRs had higher basal temperature and their temperature decreased more rapidly when exposed to 4 degrees C than temperature of controls. During exposure to 37 degrees C for 2 hrs no controls but majority of SHRs died. Treatment with clonidine (1 mg/kg, b.i.d., 14 days), hydralazine (10 mg/kg, b.i.d., 14 days) or diuretics (chlorothiazide 100 mg/kg + spironolactone 10 mg/kg, q.d., 21 days) decreased blood pressure of SHRs but did not normalize their body temperatures and heat sensitivity. These results indicate thermoregulatory dysfunction in SHRs which is probably of central origin.

Distinguishing traits in the Sabra hypertension-prone (SBH) and hypertension-resistant (SBN) rats

Distinct differences in central and peripheral noradrenaline (NA) were observed in the hypertension prone (SBH) and resistant (SBN) strain, derived from the Hebrew University SABRA rats. In the medulla oblongata NA concentration was 90% higher and tyrosine hydroxylase activity 88% lower in SBN when compared to SBH, suggesting marked strain differences in NA turnover. In this area, NA-induced cAMP generation was higher in SBH than in SBN, while the hypothalamus, the reverse situation was present. The relevance of hypertension of the reciprocal cAMP changes is still uncertain. The concentration of NA in heart tissue was significantly higher in SBN than in SBH. Doca-salt treatment caused hypertension and depletion of atrial NA in SBH, but had no effect on either blood pressure or atrial NA in SBN rats. The results suggest that resistance to hypertension in SBN rats is associated with decreased NA turnover in medulla oblongata and reduced activity of cardiac neuronal sympathetic endings.

Cyclic GMP and cyclic AMP levels in median eminence, hypothalamus and pituitary gland of the rat after decapitation or microwave irradiation

Cyclic AMP and cyclic GMP content of the median eminence (ME), medial basal hypothalamus (MBH), posterior pituitary (PP) and anterior pituitary (AP) of inact male rats was measured by radioimmunoassay following decapitation or exposure to microwave irradiation (MW). Levels of both nucleotides in MW irradiated animals were higher in all three nervous tissues studied than in the AP. Following decapitation cyclic AMP levels increased strikingly in the MBH and ME, slightly in the AP, but remained unchanged in the PP. Cyclic GMP levels increased more markedly in the ME than in the MBH, slightly in the PP and did not change in the AP. The distinct synthesizing capability of the cyclic AMP and cyclic GMP generating systems in the ME, a region rich in neurohormones known to control anterior pituitary function, raises the possibility that these nucleotides are involved in the process of neurohormone secretion by the ME.