Collagen-mediated platelet aggregation: the role of multiple interactions between the platelet surface and collagen

Although the requirement for collagen fibrils to initiate platelet aggregation is well established, there has been no satisfactory explanation for this requirement. One possibility is that multiple simultaneous and linked interactions between collagen and the platelet surface must occur to initiate the release reaction and subsequent aggregation. Direct evidence in support of this proposal was obtained by examination of the ability of collagen crosslinked in a random manner with glutaraldehyde to initiate platelet aggregation. Collagen crosslinked with 0.25% glutaraldehyde is only a slightly less effective aggregating agent than native fibrillar collagen. Further studies revealed that whereas native triple helical cross-linked collagen is an effective aggregating agent, denatured crosslinked collagen is ineffective. It thus appears that crosslinking of platelet receptor sites by multiple simultaneous and linked interactions with a rigid collagen matrix is required to initiate platelet aggregation. The precise steric relationship of the collagen sites does not appear to be of great importance.     

The role of plasma renin activity in evaluating the adequacy of mineralocorticoid replacement in primary adrenal insufficiency

BACKGROUND Elevation of plasma renin activity (PRA) is a feature of mineralocorticoid deficiency in patients with primary adrenal insufficiency. This study was designed to assess the usefulness of PRA as an index of adequacy of fludrocortisone (FC) replacement in patients with primary adrenal failure, paying particular attention to the variability in PRA levels during FC and glucocorticoid treatment. METHODS Twenty-two patients with mineralocorticoid deficiency due to primary adrenal disease were studied at 3 time points: 8, 24 and 32 hours following the administration of FC replacement. Body weight, blood pressure while supine and erect, PRA, and plasma or serum levels of aldosterone, urea, sodium and potassium were measured at each time. The clinical and biochemical consequences of adjusting the FC dose were monitored in 5 patients with PRA levels above the range seen in normal subjects and in one hypokalaemic patient with normal PRA levels. RESULTS At 8 and 32 hours following FC administration, PRA levels were not significantly different. PRA levels were significantly higher at 32 hours following FC administration (4.7 ±1.1 nmol/l/h) than at 24 hours (4.2 ±1.1 nmol/l/h, mean ± SEM, P <0.05). At 8 and 32 hours following FC administration, potassium levels were similar. Potassium levels were significantly higher at 32 hours following FC administration (3.9 ± 0.1 mmol/l) than at 24 hours (3.6 ±0.1 mmol/l, P < 0.05). No changes in measurements of sodium, urea, mean supine and erect arterial pressure or body mass index were noted at the different study points. Attempted lowering of elevated PRA in 5 normokalaemic subjects by raising the dose of FC led to normalization of PRA in all of these patients but 2 developed hypokalaemia and oedema. Lowering of FC dose in one hypokalaemic patient with normal PRA levels led to the PRA levels rising to a supranormal value while the hypokalaemia was corrected. CONCLUSIONS These results indicate that when plasma renin activity is estimated in patients with primary adrenal insufficiency replaced with daily doses of fludrocortisone, the time of day of blood sampling is not critical. Lowering elevated plasma renin activity levels to normal in patients who were considered to be otherwise normal may lead to over-treatment in some patients. Therefore, optimal fludrocortisone replacement may be associated with mildly elevated plasma renin activity levels. The information obtained by monitoring plasma renin activity adds little to the assessment of patients based on clinical evaluation and measurement of urea and electrolyte levels in blood.     

Urological manifestations of the popliteal pterygium syndrome

We report a case of the popliteal pterygium syndrome resulting in abnormalities of the external genitalia and testicular ectopia. Management included bilateral orchiopexy and complex genitoplasty. Pterygia represent errors in development that manifest as webs across joints and can result in anomalies of the external genitalia. The genitourinary aspects of the popliteal pterygium syndrome and their management are discussed.     

Breast feeding promotion in an urban and a rural Jamaican hospital

Breast feeding promotion has been a national priority in Jamaica since the mid-1970s. Despite this effort, breast feeding rates have continued to decline there, especially in urban areas. Studies of the role of health professionals in promoting breast feeding have shown that specific practices encourage breast feeding, while others discourage it. In the context of declining breast feeding in a nation committed to promoting it, the goal of this study was to explore the relationship between specific health professional practices, mothers' breast feeding, and mothers' knowledge of breast feeding in rural and urban Jamaica. To accomplish this goal, a structured interview was administered to 113 mothers of infants age 0-6 months at one urban (n = 62) and one rural (n = 51) hospital, regarding (1) physician and nurse practices known to affect breast feeding, (2) mothers' own breast feeding practices, and (3) mothers knowledge of breast feeding issues. Physician and nurse visits were also directly observed to confirm responses given to the questionnaire and to assess the resources devoted to teaching mothers about breast feeding. While extensive lectures, posters and pamphlets promoting breast feeding were provided for mothers at the urban hospital, far fewer educational resources were available for mothers at the rural hospital. Overall, however, health professional practices discouraging breast feeding were observed more frequently at the urban hospital than at the rural hospital, whereas practices promoting breast feeding were more common at the rural hospital. At the rural hospital, mothers' breast feeding practices more closely approximated recommendations than at the urban hospital.(ABSTRACT TRUNCATED AT 250 WORDS)