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Biomedical subjects

R G Clark

Publications and source records attributed to R G Clark.

At least 145 records · Page 8Linked to original sources
PubMed1978

The linear regression of body weight and age in intact, ovariecotomised, and estrogen treated rats: some applications and implications.

Many variables, including rat body weight (BWt), are sequentially measured in individuals yet the information obtained is often poorly utilised. Many advantages result if a linear relationship is established, on the original or transformed scales, between the variable and time. For individual rats log BWt, which is normally distributed, is linearly related to the reciprocal of age. Slopes (rates of BWt gain) and constants (ultimate BWts) then serve as data. Linearity extended from 4 weeks onwards in ovariectomised (OvX) and intact rats, implying that puberty does not affect BWt and that BWt increases before puberty following pre-pubertal OvX; the ovary inhibiting growth before puberty. For individual rats weaning BWt was correlated with rate of BWt gain but not with ultimate BWt, indicating postweaning compensatory growth which continues to maturity. Pre-treatment and post-treatment measurements were made on individuals, allowing within-animal comparisons and regression. Thus the BWt response to OvX or estrogen treatment depended on the pre-treatment rate of BWt gain and ultimate BWt, implying that the BWt response entails a form of compensatory growth. OvX at three ages (day 2, week 4, and week 7) produced different rates of BWt gain but similar ultimate BWts. These results support the hypothesis that ultimate BWt is predetermined, but can be modified by treatment.

Aging↗
PubMed1977

Changes in plasma lactate, phosphate and uric acid during postoperative carbohydrate infusion.

Eighteen patients undergoing elective abdominal surgery had pre- and postoperative carbohydrate infusion tests with glucose, fructose or sorbitol. All three substrates produced significant hyperlactataemia postoperatively, the elevations of plasma lactate with fructose and sorbitol infusion being significantly greater than with glucose. Plasma uric acid was unchanged but there were moderate falls in plasma phosphate postoperatively. Intravenous nutritional regimens containing fructose and sorbitol may potentiate the development of harmful metabolic acidoses in 'at risk' patients and should always be used cautiously. Glucose is the carbohydrate calorie source of choice.

Abdomen↗
PubMed1977

Changes in the proportions of plasma insulin, proinsulin and a higher-molecular-weight insulin during pre- and post-operative glucose-infusion tests.

1. Glucose-infusion tests were performed on patients admitted for elective upper abdominal surgery 1 day before and 1 day after operation. In addition to insulin and proinsulin, a third immunoreactive insulin species of mol. wt. 20 000--30 000 was detected in plasma from two patients. The heterogeneity of plasma immunoreactive insulin (IRI) and the need to consider the effects of all forms, including proinsulin and the high-molecular-weight species, is emphasized. 2. During preoperative glucose infusions there was an increase in the percentage of the total plasma IRI present as high-molecular-weight forms (i.e. proinsulin plus the species of mol. wt. 20 000--30 000) from 3.9% to 10.8%. On the first postoperative morning all patients showed an increase in the amounts of the heavier IRI types, which accounted for 13.9% of the total plasma IRI. 3. The changes in insulin and proinsulin are consistent with the release from the pancreas of an insulin/proinsulin mixture of constant proportions, and the longer circulating half-life of proinsulin. 4. Increases in the amounts of high-molecular-weight IRI species after surgery may have a partial role in the development of insulin resistance but are probably not a major determinant of the insulin-resistant state.

Adult↗
PubMed1977

Nitrogen-sparing effect of different feeding regimes in patients after operation.

In patients recovering from surgery, water, electrolytes, protein and calories all produce significant nitrogen sparing whether given by i.v. or intraduodenal routes. The nitrogen-sparing effect of protein and calories is greater when given to these patients via the gastrointestinal tract, and nitrogen equilibrium is approached when nutrients are supplied in amounts that satisfy theoretical requirements. I.v. regimes do not achieve nitrogen equilibrium, even when amino acids and calories are supplied in amounts that exceed theoretical requirements.

Adult↗
PubMed1977

Plasma insulin and surgery. I. Early changes due to operation in the insulin response to glucose.

The effects of elective abdominal operation on the disposal of a sustained intravenous glucose load and on the biphasic response of plasma insulin have been examined. During operation, low plasma insulin concentrations were observed despite the high plasma glucose values achieved. On the morning after operation, both phases of the insulin response to glucose were increased. This increase was seen even when subjects were compared at the same plasma glucose value. The response to tolbutamide was also greatly exaggerated. Pre- and postoperative glucose curves were approximately parallel, suggesting that glucose uptake was similar in both situations despite the presence of the postoperative hyperglycemia and hyperinsulinemia. This is at variance with previous reports based on conventional bolus dose intravenous tests which have suggested reduced postoperative glucose utilization. A new interpretation of the data is proposed.

Abdomen↗
PubMed1977

Plasma insulin and surgery. II. Later changes and the effect of intravenous carbohydrates.

Long-term hyperinsulinemia and improved glucose tolerance were produced postoperatively by intravenous feeding with glucose or sorbitol. Raised immuno-reactive insulin (IRI) values persisted eight hours after carbohydrate infusions although the basal plasma glucose concentrations had returned to control values. Plasma glucose curves were normal at this time but were associated with an increased IRI response. These findings suggest that insulin secretion is modified by glucose not only in the short term but also by a separate effect acting over many hours. The combination of starvation and low dose glucose infusion to simulate the hyperglycemia of operation also produced high IRI values but these were associated with a rapid fall in the plasma glucose curve. Starvation alone reduced basal values of plasma glucose and IRI, and the IRI response to glucose infusion was also reduced, despite the plasma glucose curve being at a higher level. It is suggested that the high values of IRI reported in the postoperative period are mediated by a long-term effect of the small but sustained rise in basal plasma glucose. This specific role of glucose in the long-term potentiation of insulin secretion make it the carbohydrate of choice for the intravenous feeding in postoperative patients.

Abdomen↗
PubMed1976

The relationship of plasma glucagon to the hyperglycaemia and hyperinsulinaemia of surgical operation.

In a controlled metabolic study of 42 patients undergoing abdominal surgery a significant increase in basal values of immunoreactive glucagon (IRG) was found 24 hours postoperatively. No correlation between the onset and duration of hyperglycaemia and the increase of IRG was observed. No increase in immunoreactive insulin (IRI) was seen during operation, but there was a rise 24 hours postoperatively. The infusion of arginine was accompanied by a rise in IRG both pre-and postoperatively, but despite the high values obtained there was no accompanying further increase in basal plasma glucose in the postoperative situation. The pre- and postoperative IRI responses were similar. Our evidence suggests that glucagon is not a primary mediator of the stress response, or of the hyperglycaemia of surgical operation in these patients.

Adult↗