Microcirculatory and vascular smooth muscle behavior in the Brattleboro rat: relationship to reticuloendothelial system function and resistance to shock and trauma

Impaired microvascular vasoconstrictive responses to vasopressin in septic rats

OBJECTIVE

To evaluate mechanisms of vasodilation in sepsis by comparing responses of resistance arterioles to vasopressin in rat cremaster muscle of septic and control rats.

DESIGN

Prospective, experimental study.

SETTING

Experimental animal laboratory.

SUBJECTS

Twenty male rats, anesthetized with ketamine and acepromazine.

INTERVENTIONS

Topical superfusion of vasoactive compounds on skeletal muscle resistance arterioles.

MEASUREMENTS AND MAIN RESULTS

The effect of sepsis on responses to local application of vasopressin was investigated using in vivo videomicroscopy. Vasopressin was superfused topically on the cremaster muscle resistance arterioles (15 to 25 microns) of rats made septic by cecal ligation and puncture, and the responses were compared with the responses of controls that underwent sham ligation. Responses to topically suffused vasopressin were also assessed in septic and control rats, before and after superfusion of the muscle with the nitric oxide synthase inhibitor NG-methyl-L-arginine (NMA). Sepsis produced a decrease in the vasoconstrictive effects of vasopressin; the maximal response was lower, and the concentration-response curve was shifted to the right in septic rats (p < .05). Contractions at vasopressin concentrations of 0.01, 1, and 10 nM were 39%, 36%, and 40%, respectively, of sham controls. Superfusion of the muscle with NMA partially restored arteriolar responsiveness in the septic rats, significantly increasing the arteriolar constriction of the septic rats in response to vasopressin. This effect was reversed with superfusion of excess L-arginine (1 mM).

CONCLUSIONS

This study illustrates the reduced responsiveness of the resistance arterioles of septic rats in response to vasopressin in vivo, and the partial restoration of responsiveness by concurrent application of NMA. In previous studies using this model, we have shown similar results using norepinephrine and endothelin-1, as well as angiotensin II. These findings, and the findings of this study, suggest a generalized abnormality in responsiveness of resistance arterioles to endogenous vasoconstrictors in sepsis. Partial reversal of this abnormality with NMA supports an important role for nitric oxide in mediating abnormal vasopressor responsiveness in sepsis.

Desamino-8D-arginine vasopressin treatment of Brattleboro rats: effect on sensitivity to pressor hormones

The cardiovascular effects of intravenous injections of vasopressin, angiotensin II and noradrenaline were studied in anaesthetized adult male Brattleboro rats with hereditary diabetes insipidus on lifelong treatment with the vasopressin V2 receptor agonist desamino-8D-arginine vasopressin in the drinking fluid, which restored fluid input and output to normal rat values. The pressor response to 20 ng.kg-1 vasopressin was significantly greater (P < 0.005) in the vasopressin V2 receptor agonist-treated rats than in the control animals, but the responses to all higher doses of the peptide were comparable. Doses of noradrenaline from 40 to 160 ng.kg-1 had similar pressor effects in the treated and control rats, while the pressor response to the highest dose of noradrenaline (320 ng.kg-1) was significantly lower (P < 0.01) in the vasopressin V2 receptor agonist-treated rats. Furthermore the pressor responses to all three doses of angiotensin II (40, 80 and 160 ng.kg-1) were significantly attenuated in the treated rats compared to the control group (P < 0.001, P < 0.05 and P < 0.0005 respectively), as were the decreases in heart rate (P < 0.005 at 40 ng.kg-1, P < 0.01 at 80 ng.kg-1). The hypovolaemic stimulus induced by a blood loss of 20 ml.kg-1 resulted in a lower mean arterial blood pressure initially in the treated Brattleboro rats, but subsequent recovery was similar in both treated and control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular interactions between vasopressin, angiotensin and noradrenaline in the Brattleboro rat

1. The cardiovascular effects of bolus intravenous injections of vasopressin, angiotensin II and noradrenaline were studied in 6-hydroxydopamine pretreated, anaesthetized Brattleboro rats with hereditary diabetes insipidus and normal rats of the parent Long Evans strain. 2. Pretreatment with 6-hydroxydopamine did not significantly affect control values for mean arterial blood pressure, cardiac output or total peripheral resistance in either Brattleboro or Long Evans rats but the pressor response to haemorrhage was reduced in both strains compared to the control animals. 3. The pressor responses of the untreated Brattleboro rats to 250 mu kg-1 vasopressin were significantly greater and more prolonged than in control rats of the Long Evans strain. 4. Pretreatment with 6-hydroxydopamine significantly enhanced the peak pressor response to vasopressin, but not to angiotensin II (1 microgram kg-1), in Brattleboro and Long Evans rats. 5. Pretreatment with 6-hydroxydopamine resulted in an enhanced pressor response to 1 microgram kg-1 noradrenaline in both Brattleboro and Long Evans rats, but the effect was significantly greater in the vasopressin-deficient animals. 6. These results indicate differences in the pressor responsiveness of Brattleboro rats to vasopressin and noradrenaline, but not to angiotensin II, compared with control Long Evans rats and provide evidence for important interactions between the sympathetic nervous system and these pressor hormones.

Comparison of the development of experimental pyelonephritis in homozygous brattleboro diabetes insipidus rats, heterozygous control rats and normal Wistar rats

A comparative study was performed on haematogenous experimental pyelonephritis by injecting a Staphylococcus aureus suspension i.v. to homozygous and heterozygous Brattleboro and Wistar rats. The numbers of viable bacteria in blood, urine and kidney homogenates and the pathomorphological scores determined on the tenth day of infection were significantly lower in Brattleboro diabetes insipidus rats than in heterozygous Brattleboro and normal Wistar rats. The results suggest that homozygous Brattleboro rats are much more resistant to experimental pyelonephritis.

Altered baroreceptor inputs to the supraoptic nucleus of the Brattleboro rat

In Brattleboro rats, many more supraoptic neurones are baroresponsive than in normal rats. This may reflect the more widespread noradrenergic innervation of the supraoptic nucleus in Brattleboro rats. If so, the present data suggest that baroreceptor influences on vasopressin secretion are mediated by a noradrenergic pathway and that the altered responsiveness reflects the altered innervation.