Cosecretion of calcitonin gene products: studies with a C18 cartridge extraction method for human plasma PDN-21 (katacalcin).

PDN-21, the carboxyl-terminal flanking peptide encoded by the calcitonin (CT) gene, has been found in plasma of patients with medullary thyroid carcinoma and reportedly is cosecreted with CT. To test whether PDN-21 and CT are cosecreted in normal subjects, we developed a RIA for PDN-21 and measured immunoreactive CT and PDN-21 in whole plasma and silica or C18 cartridge extracts of plasma (exCT, exPDN-21) before and after calcium (Ca) infusion (2 mg Ca/kg over 5 min) in nine normal men and nine normal women. Plasma CT and immunoreactive PDN-21 levels were often below the assay detection limits. In contrast, basal exCT and exPDN-21 were detectable in all plasma samples, and the concentrations of both were significantly higher in men than in women [basal exCT (mean +/- SE): men, 4.8 +/- 0.3 ng/L; women, 2.4 +/- 0.3 (P less than 0.001); basal exPDN-21: men, 4.7 +/- 0.3 ng/L; women, 3.3 +/- 0.3 (P less than 0.01)]. Ca infusion sharply increased CT and PDN-21 concentrations in both sexes, but the increments were greatest in men [mean (+/-SE) increment of exCT: men, 37.2 +/- 3.9 ng/L; women, 15.7 +/- 4.3 (P less than 0.002); mean increment of exPDN-21: men, 29.7 +/- 4.7 ng/L; women, 11.0 +/- 3.1 (P less than 0.005)]. The molar concentrations of exCT and exPDN-21 were closely correlated (r = 0.97; P less than 0.001). With our antiserum, the extraction-concentration technique for measurement of PDN-21 had increased sensitivity and decreased nonspecific interference compared to the whole plasma assay. We conclude that CT and PDN-21 are cosecreted from normal thyroid C-cells under the control of extracellular fluid Ca, and that men have greater secretory capacity for both peptides than women. Plasma PDN-21 may serve alternatively to CT as a marker for C-cell activity.

Effects of systemic delivery of insulin on plasma lipids and lipoprotein concentrations in pancreas transplant recipients.

OBJECTIVE: To determine whether pancreas transplantation alters lipid and lipoprotein concentrations and whether peripheral hyperinsulinemia is always associated with altered lipid levels. DESIGN: We assessed the lipid profiles of seven pancreas-kidney recipients with insulin-dependent diabetes mellitus, seven kidney recipients without diabetes who received the same immunosuppressive agents, and eight normal subjects. MATERIAL AND METHODS: In the three study groups, fasting and postprandial plasma glucose, insulin, C-peptide, cholesterol, triglyceride, free fatty acid, and apolipoprotein A-I, A-II, C-II, and C-III concentrations were determined. RESULTS: Fasting and postprandial glucose concentrations did not differ between the two transplant groups; however, peripheral insulin concentrations were twice as high (P < 0.05) in the pancreas-kidney recipients as in the kidney recipients both before (102 +/- 15 versus 53 +/- 6 pmol/L) and after (123 +/- 22 versus 61 +/- 6 nmol/L per 6 hours) ingestion of a meal. Preprandial and postprandial insulin levels in both transplant groups also were greater (P < 0.05) than those in normal subjects (35 +/- 6 pmol/L and 40 +/- 7 nmol/L per 6 hours, respectively). Despite significant differences in insulin concentrations, no differences were noted in total cholesterol, high-density or low-density lipoprotein cholesterol, plasma free fatty acids, or apolipoprotein A-I, A-II, C-II, and C-III concentrations among the study groups. Plasma triglyceride concentrations in the two transplant groups were similar (114 +/- 20 versus 142 +/- 18 mg/dL) and were slightly more than those in the normal subjects (80 +/- 7 mg/dL). CONCLUSION: Despite peripheral hyperinsulinemia, pancreas transplantation can result in normal or near-normal lipid and lipoprotein concentrations. Thus, systemic delivery of insulin does not invariably produce an atherogenic lipid profile.

Insulin-like growth factor-binding protein-1 response to insulin during suppression of endogenous insulin secretion.

Insulin-like growth factor-binding protein-1 (IGFBP-1) is one of several related proteins that bind and modulate the actions of IGFs. The liver is the primary source of IGFBP-1, and insulin is a major regulator of hepatic IGFBP-1 production. We report five sets of investigations that further define the characteristics of hepatic IGFBP-1 response to insulin. In normal subjects, a continuous high-dose insulin infusion caused a rapid decrease in plasma IGFBP-1 concentrations, with a rate of 0.24 +/- 0.04 microgram/L.min-1 and a t1/2 of 89 +/- 4 minutes. Conversely, a 3-hour somatostatin (SRIF) infusion caused a 4.5-fold increase in plasma IGFBP-1 levels. SRIF plus low-dose insulin infusion (to inhibit break-through insulin secretion) resulted in a plateau in IGFBP-1 concentrations at 5 to 8 hours, with a t1/2 to achieve steady state of 60 to 75 minutes. Under similar conditions, a stepped increase in plasma glucose level from 5 to 9 mmol/L had no effect on the rate of IGFBP-1 increase in plasma, indicating that an acute increase in glucose concentration within a physiologic range has no independent inhibitory effect on IGFBP-1 production in the presence of a nonsuppressive insulin level. Using SRIF plus sequential graded insulin infusions, the threshold peripheral (= portal) plasma insulin concentration for IGFBP-1 suppression was between 65 and 172 pmol/L. Subjects with insulin-dependent diabetes mellitus (IDDM) showed a similar dose-response pattern, suggesting that insulin regulation of IGFBP-1 may be normal in IDDM.(ABSTRACT TRUNCATED AT 250 WORDS)

A hypothesis for the formation of vertical corneal striae as observed in the wearing of softlens contact lenses and in keratoconus.

It is postulated that vertical striae are created in the central corneal area by way of mild edema in the posterior layers, which causes a buckling in the shorter, thinner vertical meridia.