A new guanidine derivative: dissociation of the adrenergic neuron blocking activity from local anesthetic activity

Pelvic afferent reflex control of rectal motility and lumbar colonic efferent discharge mediated by the pontine sympatho-inhibitory region in guinea pigs

Rectal motility and the efferent discharge of lumbar colonic nerves (LCED) have previously been shown to be affected by reflex activity activated by rectal stimulation. The sensory limb of this reflex is represented by afferent fibers in pelvic nerves. The present study revealed that this reflex is modulated by supraspinal sympatho-inhibitory regions. Pelvic afferent stimulation led to rectal contraction through the withdrawal of a tonic inhibitory influence of lumbar colonic nerves. The supraspinal region responsible for this antagonism of the rectal-inhibitory colonic nerve activity was localized to the pons. Neither the intravenous administration of atropine nor that of guanethidine (and Eisai compound 865-123, another adrenergic neuron blocking agent) effected the ability of pelvic afferent stimulation to inhibit tonic discharge of lumbar colonic efferent nerves; nevertheless, both agents eliminated the mechanical response of the rectum to stimulation of pelvic afferents. These observations suggest that lumbar sympathetic nerves may tonically inhibit the release of acetylcholine from excitatory neurons in the rectal myenteric plexus. We conclude that descending fibers from the pons are activated as a result of pelvic afferent nerve stimulation. These descending pontine fibers in turn inhibit the firing of sympathetic lumbar colonic nerves. Removal of this tonic restraint leads to rectal contraction.

Role and localization of a region in the pons which has a descending inhibitory influence on sympathetically mediated inhibition of the recto-rectal reflex of guinea pigs

The present study revealed the site of origin and the possible function of a supraspinal descending-inhibitory influence over the lumbar sympathetic component of the recto-rectal reflex of guinea pigs. The recto-rectal reflex contraction was not changed by suprapontine transection. It completely disappeared after subpontine transection, but returned immediately after additional section of the colonic nerves, which contain the sympathetic inhibitory outflow to the rectum, i.e., subpontine transection with the lumbar colonic nerves transected did not suppress the recto-rectal reflex. These results indicate that a descending pathway which can inhibit the lumbar sympathetic component of the reflex may originate in the pons. On stimulation at sites within the pons of animals which had been spinalized at L4 we were able to evoke an increase of rectal motility and an inhibition of the lumbar colonic efferent discharges, thus producing a response which is comparable to the reflex response produced by afferent stimulation of the rectum. The sites from which this effect could be evoked were mainly located in a band running rostrocaudally through the lateral reticular formation of the rostral part of the pons, medial to the sensory nucleus of the trigeminal nerve.

Comparative studies of (--)-, (+/-)-propranolol, atenolol, guanethidine, bretylium and tetracaine on adrenergic transmission

1 Effects of (--)-, (+/-)-, and (+)-propranolol, atenolol, guanethidine, bretylium and tetracaine were studied on relaxation responses of rabbit ileum and contractile responses of rabbit pulmonary artery and guinea-pig vas deferens to electrical nerve stimulation (2 to 50 Hz). 2 In the ileum, inhibition by tetracaine 3.3 x 10(-6) M occurred at high frequencies of stimulation, while bretylium 1.2 x 10(-4) M and guanethidine 2 x 10(-5) M inhibited responses at all frequencies, the latter producing greater inhibition at low frequencies. 3 (+/-)-Propranolol 10(-5) M produced a tetracaine-type inhibition after 1 h and a bretylium-pattern after 2 h in the ilea and pulmonary arteries and a transition from bretylium- to guanethidine-pattern in the vas deferens, while atenolol 2 x 10(-5) to 10(-4) M produced guanethidine-type inhibition in all preparations. 4 (--)-, (+/-)-, and (+)-Propranolol 3 x 10(-6) to 3.3 x 10(-5) M were equipotent in the vas deferens and ileum. However, inhibition by (--)-propranolol 3.3 x 10(-5) M persisted in the ileum, while that by the (+)-isomer was partially restored by washing. 5 (--)- or (+)-Propranolol 3.3 x 10(-5) M or atenolol 2 x 10(-5) M did not inhibit relaxation of the ileum after the bath temperature was maintained at 4 degrees C for 2 h during drug application. 6 In conclusion, propranolol and atenolol both have gradually developing guanethidine-like adrenergic neurone blocking actions.

Further evidence for the prevention by guanethidine of noradrenaline efflux from rabbit ventricular slices induced by a low external sodium concentration

When guanethidine was applied to rabbit ventricular slices at 37 degrees C for an initial 30 min incubation period, doses of 4 X 10(-5) and 8 X 10(-5) M irreversibly inhibited increases in efflux of noradrenaline induced by the subsequent reduction of external sodium concentrations to 18 mM. This inhibition was prevented if the temperature was reduced to 0 degrees C during the drug application period. Guanethidine transported into adrenergic nerve endings appears to increase permeability to Na+, thereby leading to the reduction in efflux.

Prevention by guanethidine analogues of output of noradrenaline induced by sodium reduction in rabbit ventricular slices

1 The prevention by guanethidine and related agents of the output of noradrenaline induced by low sodium was investigated in rabbit ventricular slices. When external NaCl was reduced, the output of noradrenaline into the medium collected at 30 min intervals, increased and the endogenous levels decreased. These changes induced by replacing sodium with sucrose or choline were not affected either by the omission of calcium and addition of 0.5 mM ethylene glycol-bis(aminoethylether)N,N,N',N' tetra-acetic acid (EGTA) or by an increase in the calcium concentration to 10 mM 30 min before sodium deprivation.2 Guanethidine 4 x 10(-6) and 4 x 10(-5) M and 4-7-exo-methylene-hexahydroisoindoline-ethyl guanidine (No. 865-123) 4 x 10(-5) to 8 x 10(-4) M inhibited, in a dose-dependent manner, increases in output of noradrenaline induced by reduction of sodium to 18 mM, while guanethidine 8 x 10(-5) M and high doses of bretylium produced no inhibition: the latter two released noradrenaline.3 The inhibitory actions of guanethidine 4 x 10(-5) M and No. 865-123 4 x 10(-4) M were prevented by tetracaine 3.3 x 10(-4) M, which per se did not modify the output of noradrenaline induced by 18 mM sodium.4 Accumulation of guanethidine and No. 865-123 in ventricular slices was greater than that noted in striated muscle slices and was dose-, time- and temperature-dependent. Tetracaine 3.3 x 10(-4) M did not prevent the accumulation of guanethidine 4 x 10(-5) M and No. 865-123 1.1 x 10(-6) to 4 x 10(-4) M.5 The guanidine derivatives appear to increase the permeability of adrenergic nerve endings to sodium ions.

Action of guanethidine on rabbit atrial membranes

1 Intracellular potentials were recorded in driven left atria from reserpine-treated rabbits. Guanethidine 2 X 10(-5) M slightly increased Vmax and shortened the total duration (TD) of the action potential (AP) without causing hyperpolarization. For the first 30 min after 4 X 10(-4) M, Vmax increased without hyperpolarization and AP height increased slightly. Thereafter, Vmax and height decreased with a slight and gradual depolarization. This depolarization was irreversible. TD was increased after 15 minutes. Guanethidine 2 X 10(-3) M initially decreased Vmax and height before causing depolarization. 2. Pretreatment with tetrodotoxin (TTX) 1.6 X 10(-7) M prevented or reversed the initial increases in Vmax, height and TD induced by guanethidine (4 X 10(-4) M). 3 TTX 3.1 to 6.2 X 10(-6) M, added 15 or 30 min after guanethidine 4 X 10(-4) M, delayed or prevented depolarization by guanethidine. 4 Ouabain 10(-5) M incubated for 20 and 90 min greatly inhibited Na+, K+-adenosine triphosphatase and K+-phosphatase activities; guanethidine was without effect. 5 Guanethidine probably increases resting sodium permeability after the promotion of increases in sodium permeability during the AP. High doses of the drug decrease sodium permeability during the AP.