Vascular resistance in the perfused isolated rat tail

Cinnamaldehyde application decreases tail temperature in ovariectomized rats with and without estradiol administration

The aim of this study was to examine the effect of estradiol (E₂) on the thermoregulatory responses induced by cinnamaldehyde, a component extracted from cinnamon at 16 °C or 27 °C. The thermoneutral and subneutral experiments were performed to evaluate the augmented effect of cinnamaldehyde by cold exposure and the effect of cinnamaldehyde itself. Ovariectomized rats were implanted with a silastic tube with or without E₂ (E₂(+) and E₂(-) groups), and data loggers into the peritoneal cavity. After the application of 30% cinnamaldehyde or vehicle into the skin of the whole trunk of rats, the rats were exposed to 16 °C or 27 °C for 2 h. Body temperature (T_b) and tail temperature (T_tail) were measured using a data logger and thermography. After exposure, blood samples were obtained, and plasma catecholamine concentration were measured by high-performance liquid chromatography. In the E₂(-) group exposed to 27 °C, the change in T_b in rats applied cinnamaldehyde was significantly lower than that of rats applied vehicle. The change in T_tail in rats applied cinnamaldehyde was significantly lower than that of rats applied vehicle in both E₂(-) and E₂(+) groups at 27 °C and 16 °C. Plasma catecholamine concentration at 27 °C was not different among the groups. E₂ might not affect thermoregulatory responses induced by cinnamaldehyde application; however, it decreased T_tail in female rats.

Evidence for prazosin-resistant, rauwolscine-sensitive alpha-adrenoceptors mediating contractions in the isolated vascular bed of the rat tail

1. The postjunctional alpha-adrenoceptors mediating contractions in the isolated vascular bed of the perfused rat tail have been investigated, in the presence and absence of an increase in perfusion pressure by arginine vasopressin (AVP). 2. In the absence of AVP, bolus doses of noradrenaline (NA) and phenylephrine produced pressor responses of similar time course, while UK-14,304 was practically inactive. Responses to noradrenaline were inhibited more by 0.05 microM prazosin than by 1 microM rauwolscine, suggesting the presence of alpha1-adrenoceptors. 3. Following a sustained elevation in perfusion pressure by AVP, both UK-14,304 and NA (the latter in the presence of 0.05 microM prazosin to inhibit alpha 1-adrenoceptors) elicited dose-dependent pressor responses. The maximum response to UK-14,304 under these conditions was approximately 30% of the maximum response to NA in the absence of prazosin and AVP. Responses to phenylephrine were not affected by the AVP-induced increase in vascular tone. 4. In the presence of AVP, pressor responses to UK-14,304 were resistant to 0.05 microM prazosin and susceptible to antagonism by 1 microM rauwolscine (-log Kb 7.65 +/- 0.15). Similarly, responses to NA in the presence of 0.05 microM prazosin and AVP were inhibited by 1 microM rauwolscine. This represents the first demonstration of prazosin-resistant, rauwolscine-sensitive alpha 2-adrenoceptor-mediated responses in the vasculature of the rat tail. 5. These results suggest that in isolated vascular preparations, functional populations of postjunctional alpha 2-adrenoceptors may be 'uncovered' by the presence of AVP.

The innervation of the caudal artery of the rat

The sympathetic innervation of the main ventral artery of the rat tail has been studied using electrophysiological, histochemical and biochemical techniques. Excitatory junction potentials were evoked in the smooth muscle cells of an isolated segment (1-2 cm long) of the proximal vessel by stimulating its proximal end with a suction electrode. The amplitude of these potentials decreased distally until they were undetectable 6-8 mm from the stimulating electrode. The density of noradrenergic terminals along the length of the vessel was examined using formaldehyde-induced fluorescence and assay of endogenous noradrenaline, before and after lesioning the perivascular nerve plexus by freezing, or dividing the dorsal and ventral collector nerves. The results show that sympathetic axons run along the artery to make functional contact over only a few mm. Most (about 80%) of the sympathetic supply reaches the vessel after branching from the ventral collector nerves; the rest arises via the dorsal collector nerves. The location of the cell bodies of origin of the axons in the collector nerves has been identified after retrograde labelling with horseradish peroxidase. Motor and sensory axons in both dorsal and ventral nerve trunks arose from segments S2 to Co3, while almost all sympathetic neurons (95-98%) projecting to the tail were located in paravertebral ganglia S1 to S4 and the coccygeal ganglion. These results provide the first description of the relationship of the sympathetic innervation of the rat tail to its motor and sensory supply.

The effects of etilefrine on blood vessels in the rat tail

Etilefrine was found to constrict blood vessels in the rat tail through a mechanism which was partly dependent on the sympathetic nerves present in these vessels. The response to the drug was enhanced by pretreagment with noradrenaline and cocaine, and totally abolished by the alpha-receptor antagonist phentolamine. When compared with several other sympathomimetic agents which were tested on the vessel, etilefrine appeared to have a low order of vasoconstrictor activity. These findings would seem to have considerable relevance to the clinical situation where an attempt has been made to use etilefrine in the treatment of patients with orthostatic hypotension.

Anti-inflammatory property of 401 (MCD-peptide), a peptide from the venom of the bee Apis mellifera (L.)

1 Peptide 401, a potent mast cell degranulating factor from bee venom, substantially inhibited the oedema provoked by subplantar injection of carrageenin or intra-articular injection of turpentine in the rat. The ED(50) of 401 was c. 0.1 mg/kg. The anti-inflammatory effect was assessed by measurement of the increased (125)I-albumin content of an injected site in comparison with an uninjected contralateral site.2 Peptide 401 also suppressed the increased vascular permeability due to intradermal injection of various smooth muscle spasmogens (histamine, bradykinin, 5-hydroxytryptamine (5-HT), and prostaglandins).3 Other comparable mast cell degranulating agents (48/80 and melittin) showed little evidence of anti-inflammatory activity when tested at comparable dosage on turpentine arthritis and carrageenin oedema.4 The anti-inflammatory effects were not abolished by pretreatment with mepyramine and methysergide, which abolished the increased vascular permeability produced by local injection of 401.5 The anti-inflammatory action of 401 was not affected by regional denervation or pretreatment with phenoxybenzamine, and was reduced but not abolished by adrenalectomy.6 Measurement of skin temperature, fractional extraction of (86)Rb and blood flow in perfused mesentery gave no evidence that the anti-inflammatory action of 401 was due to reduced tissue perfusion.7 It is concluded that 401 may exert its anti-inflammatory action directly by making the vascular endothelium anergic to phlogistic stimuli.

Binding of catecholamines to connective tissue and the effect upon the responses of blood vessels to noradrenaline and to nerve stimulation

1. Quantitative estimates have been made of the binding of catecholamines to purified collagen and elastin, and the factors influencing this binding have been investigated.2. Collagen shows no specificity towards the binding of either the (-)- or (+)-isomer of adrenaline or noradrenaline, at low concentrations. Elastin binds the (-)-isomer of adrenaline and noradrenaline to twice the extent of the (+)-isomer.3. Tetracyclines inhibit the binding of catecholamines to collagen and elastin. Oxytetracycline 10(-4)M produces a maximum inhibition of the binding of (-)-noradrenaline to collagen of 68.4%.4. The responses of perfused blood vessels to the administration of pulses of catecholamines or to adrenergic nerve stimulation have been measured.5. Oxytetracycline (10(-4)M) potentiates the amplitude of the response of the rabbit ear artery to noradrenaline and to nerve stimulation, ten- and sixfold respectively.6. Those preparations with a high content of collagen and elastic tissue, the rabbit ear artery and the rat tail, are more susceptible to the potentiating effects of oxytetracycline than one with a low content, the rat anococcygeus.7. The results of the study suggest that in tissues with a high content of collagen and elastin, binding to extracellular sites is the major mechanism for terminating the response to noradrenaline or to adrenergic nerve stimulation.