David F. Biggs

Pharmacology of anatoxin-a, produced by the freshwater cyanophyte Anabaena flos-aquae NRC-44-1.

Abstract Anatoxin-a (ANTX-A) is the neuromuscular blocking agent produced by the freshwater cyanophyte Anabaena flos-aquae (Lyngb.) de Breb. strain NRC-44-1. Its pharmacological properties have been investigated and compared with that of synthetic ANTX-A which was derived from l -cocaine. ANTX-A is a potent depolarizing neuromuscular blocking agent possessing both muscarinic and nicotinic activity. Responses to ANTX-A on the isolated frog-rectus abdominus muscle were qualitatively similar to those obtained with acetylcholine, carbachol and decamethonium, with ANTX-A being the most potent. Neostigmine and tetrodotoxin failed to affect responses to ANTX-A. The affinity constant for ANTX-A on the frog-rectus preparation was 3·1 μM, compared to 1·0 μM for carbachol. On the chick biventer cervicis preparation ANTX-A was less potent but produced responses similar to that of decamethonium. d -Tubocurarine and hexamethonium caused a shift to the right in the dose-response curves of ANTX-A and decamethonium. On the isolated rat phrenic nerve-hemidiaphragm ANTX-A and decamethonium blocked the muscle twitch response which was not reversed by neostigmine. ANTX-A produced a depolarizing blockade on the cat sciatic nerve-anterior tibialis preparation which was similar but less than that produced by decamethonium. On the isolated guinea pig ileum, ANTX-A had a potency approximately the same as that of 1,1-dimethyl-4-phenyl piperazinium but less than that of acetylcholine.

Low‐dose methotrexate kinetics in arthritis

Twelve patients with either rheumatoid or psoriatic arthritis were injected with a 10‐mg bolus dose of methotrexate (MTX) either intramuscularly (n = 6) or intravenously (n = 6) and the MTX concentration in their sera was determined by radioimmunoassay. MTX concentration‐time data fitted triexponential equations. Doses injected intramuscularly were rapidly and completely absorbed. There were no significant intergroup differences in drug mean t½, volume of distribution, and total body clearance. In nine patients serum MTX concentrations remained above the suggested critical level of 0.01 µmol throughout the 24‐hr study irrespective of the route of administration, but MTX did not cumulate in the serum. We conclude that the behavior of low doses of MTX in patients with arthritis closely resembles the pattern in patients receiving intermediate and high doses for the treatment of neoplasia.

Muscarinic receptors and parasympathetic neurotransmission in guinea-pig trachea.

Muscarinic receptors involved in cholinergic neurotransmission were studied in isolated innervated guinea-pig tracheas using preganglionic (nerve) and postganglionic (field) stimulation, after blocking sympathetic effects with bethanidine (5 microM). Neostigmine (10 nM) significantly increased responses to nerve and field stimulation. The M1 antagonist pirenzepine (0.1-100 nM) selectively reduced tracheal responses to nerve stimulation in control and in neostigmine-treated tissues. The M2 antagonist gallamine (0.1-100 microM) significantly increased tracheal responses to nerve and field stimulation in control and in neostigmine-treated preparations. At concentrations that increased baseline tone, oxotremorine, arecoline and pilocarpine decreased responses to nerve and field stimulation. Gallamine (30 microM) selectively reduced the inhibitory effects of these agonists on responses to nerve and field stimulation. The findings indicate that cholinergic neurotransmission in guinea-pig trachea is modulated by facilitatory M1 receptors at parasympathetic ganglia and inhibitory M2 receptors at the postganglionic nerve endings.

Does capsaicin cause reflex bronchospasm in guinea-pigs?

Capsaicin given intravenously (i.v.) into the vena cava or intra-arterially (i.a.) into the aortic arch of anesthetized guinea-pigs induced dose-dependent increases in pulmonary-flow resistance (R) and dynamic thoracic elastance (E). Threshold doses were 0.5-1.0 micrograms/kg body weight; greater than 8.0 micrograms/kg induced tachyphylaxis. These responses to capsaicin, i.v. or i.a., were similar after decentralization, bilateral vagotomy, or glossopharyngealotomy, and after autonomic blockers (mecamylamine, atropine, mepyramine, and bethanidine). Morphine significantly reduced responses to capsaicin but had no effect on responses to substance P (SP). Naloxone did not reverse the inhibitory effect of morphine, and neither reduced nor enhanced capsaicin-induced increases. Of the two antagonists to SP examined (given i.v.), [D-Pro2,D-Trp7,9]SP had no effect on SP-induced increases but abolished capsaicin-induced increases in R, though without affecting increases in E, and [D-Arg1,D-Pro2,D-Trp7,9,Leu11]SP reduced increases in R induced by both SP and capsaicin but had no effect on increases in E. Capsaicin (2.0-32.0 micrograms/kg i.v. or i.a.) had no bronchospastic effect in guinea-pigs given this drug (50.0 mg/kg s.c.) 7 days earlier. We conclude that in guinea-pigs--unlike other species--capsaicin causes bronchospasm without stimulating any afferent receptors in a centrally mediated bronchospastic reflex arc.

Capsaicin selectively reduces airway responses to histamine, substance P and vagal stimulation

Airway responsiveness to histamine, substance P, methacholine and bilateral electrical vagal stimulation was assessed in capsaicin-treated and control guinea pigs. In animals treated with capsaicin (50 mg/kg s.c.) 7 days before experiments, airway responsiveness to histamine, substance P and vagal stimulation was significantly reduced but responsiveness to methacholine was unchanged. The findings suggest that histamine and substance P, but not methacholine, require capsaicin-sensitive sensory afferent nerves for part of their actions.

High current pulser for transmural and field stimulation

The determination of the requirements and the design of a constant current pulse generator with low internal resistance capable of providing the high currents required for transmural and field stimulation of biologic tissues are described. It is concluded that direct measurement of current flowing and voltage applied to electrodes is the best way of monitoring stimulus parameters.

AN inexpensive bipolar stimulator

The design of a pulse generator for electrical transmural stimulation is described. The device produces pulses of alternating polarity with amplitudes continuously variable up to 120 V and output currents limited to 6 mA. Pulse widths may be varied from 1 to 5 ms with repetition rates from 1.7 to 40 pulses per sec. A gate signal may be applied to inhibit output so that bursts of pulses may be generated.

Release of monokines by pulmonary macrophages following antigen challenge in sensitized guinea pigs

Guinea pigs were passively sensitized with immune serum to ovalbumin (OA), control serum, or saline. Twenty-four hours later, they inhaled aerosols of OA (2% in saline), saline, or lipopolysaccharide (LPS). Following anesthesia, bronchoalveolar lavage (BAL) was performed at 30, 60, 90 and 120 min postinhalation. Alveolar macrophages (AM) were isolated from the BAL fluid and incubated (18 h) in medium alone or with zymosan (1 mg/ml). Supernatants were collected and levels of interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) determined by bioassays. Unstimulated AM from animals that inhaled OA, saline, or LPS secreted similar amounts of IL-1 at 30, 60, and 90 min postinhalation. Zymosan (1 mg/ml) significantly increased IL-1 secretion by AM collected at 60 and 90 min from OA-sensitized animals that inhaled OA or saline. AM from guinea pigs sensitized to OA that inhaled OA or LPS secreted significantly increased amounts of IL-6 at 30, 60, 90, and 120 min postchallenge compared to saline sensitized controls. In all groups, AM from LPS-treated animals secreted large amounts of TNF-α at all sampling times postchallenge; AM from OA-sensitized and challenged animals secreted increasing amounts of TNF-α with time postchallenge, spontaneously and in response to zymosan. By contrast, AM from saline sensitized and challenged guinea pigs did not release detectable amounts of TNF-α spontaneously and secreted very low amounts in the presence of zymosan. These findings show that antigen challenge results in a rapid activation of AM isolated from BAL and suggest AM may initiate the development of inflammatory processes associated with antigen challenge.

A digital timing system for a small animal respiration pump

A digital timing system has been developed to control the airflow from a respiration pump used in small animal pulmonary measurements. Three separate periods of up to 10 sec may be selected with millisecond resolution using thumb-wheel switches. A modular design using CMOS technology minimized the number of interconnections among the various parts of the system. A larger number of timing channels, longer time periods, and greater time resolution may be achieved by directly extending the existing design.