Effect of intravenous atropine on gastric emptying, paracetamol absorption, salivary flow and heart rate in young and fit elderly volunteers.

1. The effects of atropine on gastric emptying, paracetamol absorption, salivary flow and heart rate were examined in young and elderly subjects. 2. Seven healthy young male subjects of age 23 +/- 1.3 years (mean +/- s.e. mean) and seven fit elderly subjects of age 70 +/- 1.6 years received placebo (P), 300 micrograms atropine (A300) or 600 micrograms atropine (A600) in randomized order at weekly intervals. After 10 min they ingested a 500 ml orange drink containing 1 g paracetamol. Gastric emptying was measured by ultrasound, blood samples were taken to measure plasma paracetamol concentration by h.p.l.c., salivary flow was measured by dental cotton wool cylinder technique and pulse rate was recorded. 3. In young subjects, the gastric 5 min volumes were 260.1 +/- 17.9 ml (s.e. mean) with P, 310.6 +/- 10.5 ml with A300 and 317.9 +/- 8.9 ml with A600. In elderly subjects, the gastric 5 min volumes were 166.7 +/- 10.1 ml with P, 252.6 +/- 13.7 ml with A300 and 266.0 +/- 14.8 ml with A600. Thus the early adaptive phase of gastric emptying was more rapid in the elderly than the young with all treatments (P less than 0.05). The gastric emptying half-lives were 18.8 +/- 2.5 min with P, 30.0 +/- 2.7 min with A300 and 34.5 +/- 3.3 min with A600 in young subjects (P less than 0.01). In elderly subjects, the gastric emptying half-lives were 16.1 +/- 2.5 min with P, 23.7 +/- 2.4 min with A300 and 30.0 +/- 2.9 min with A600 (P less than 0.01). Thus atropine intravenously in therapeutic dose (300 and 600 micrograms) delayed gastric emptying in both young and elderly subjects. The inhibitory effect of atropine on the early adaptive phase of gastric emptying appeared to be greater in the elderly. The maximum plasma concentration (Cmax) of paracetamol was greater in the elderly than young with all treatments (P less than 0.05). There was a close relationship between the early adaptive phase of gastric emptying and paracetamol absorption (P less than 0.05). Atropine reduced salivary flow and increased resting heart rate in both young and old subjects. The effect of atropine on salivary flow was greater in the elderly. 4. The dose-response relationship varied in the three systems (stomach, salivary glands and heart rate) studied. Age had an effect on the magnitude of the response, but not on the slope of the dose-response curve for the two doses of atropine studied.(ABSTRACT TRUNCATED AT 400 WORDS)