Factors affecting insulin-like growth factor-I concentration in bovine milk.

To establish the naturally occurring range of insulin-like growth factor-I concentrations in bovine milk, samples from individual cows (n = 409) managed on five Missouri dairy herds were assayed. Parity, stage of lactation, and farm affected milk insulin-like growth factor-I concentration. Milk insulin-like growth factor-I concentration was higher in early lactation than mid and late lactation with concentrations in multiparous cows exceeding those in primiparous cows. Insulin-like growth factor-I concentration was negatively correlated to milk production the day of sample collection (r = -.15) and not correlated to predicted 305-d milk yields. Unprocessed bulk tank milk samples (n = 100) from a commercial processing plant had a mean concentration of insulin-like growth factor-I in milk of 4.32 ng/ml with a range of 1.27 to 8.10 ng/ml. This distribution was similar to the range detected in samples from individual cows, but values were lower than those reported for human milk. Concentration of insulin-like growth factor-I in milk was not altered by pasteurization (at 79 degrees C for 45 s). However, insulin-like growth factor-I was undetectable in milk heated to temperatures (121 degrees C for 5 min) required for infant formula preparation or in commercially available infant formula. These data indicated that insulin-like growth factor-I is a normal but quantitatively variable component of bovine milk that is not destroyed by pasteurization but is undetectable in infant formula. Concentration of insulin-like growth factor-I in bovine milk is lower than concentrations reported for human milk yet similar to those reported for human saliva.(ABSTRACT TRUNCATED AT 250 WORDS)

End-expiratory volume in the rat: effects of consciousness and body position.

Functional residual capacity (FRC), tidal volume (VT), and frequency (f) were compared in 23 rats while either awake and unrestrained or anesthetized. FRC was determined from gas compression with closed airway inside a cone-shaped body plethysmograph. In the awake state (mean +/- SD), FRC was 1.02 +/- 0.22 ml/100 g, VT was 0.38 +/- 0.06 ml/100 g, and f was 142 +/- 22 breaths/min. During anesthesia, FRC decreased (P less than 0.01) to 52.9% of awake values, VT increased (P less than 0.01) to 147.4%, and f decreased (P less than 0.01) to 71.8%, leaving minute ventilation almost unchanged. An additional seven rats were used to examine postural effects on FRC during anesthesia, and in another seven animals pleural pressure changes were monitored. Dynamic lung compliance (0.80 ml . kg-1 X cmH2O-1) was not altered by anesthesia, but the pressure-volume curve was shifted 6 cmH2O higher. Thoracic compression, followed by a time-dependent effect of volume history, may account for the major change in FRC. The remainder of the decrease in FRC may be due to lower breathing frequency, loss of inspiratory muscle activity, and/or less airway resistance after anesthesia. Peak diaphragmatic electromyogram per unit VT was shown to increase almost linearly with FRC, indicating that diaphragmatic efficiency was decreased as lung volume was elevated.

Cardiorespiratory responses to sudden release of circulatory occlusion during exercise.

Cardiovascular and respiratory parameters were measured during and after release of pressure in thigh cuffs which occluded circulation to the legs of four human subjects exercising on a bicycle ergometer. The subjects exercised at 200 kg/min while thigh cuffs were inflated for 4 min and then released. Responses from 6 to 8 identical experiments were ensemble averaged so the precise timing of delays could be obtained. Five to ten seconds following cuff release, end-tidal CO2 increased, marking arrival of the trapped blood at the lungs. Ten to eighteen seconds after this increase in end-tidal CO2, ventilation, respiratory rate and tidal volume increased. This delay in ventilation must have resulted in an increase in arterial PCO2 and suggests that arterial chemoreceptors mediated the responses, and that no venous chemoreceptors or CO2-flux or disequilibrium receptors in the lung need be postulated.

Cardiorespiratory responses following isoproterenol injection in rabbits.

Receptor sites for the ventilatory response to isoproterenol were investigated in anesthetized rabbits with bolus injections in the common carotid artery (ia) and in the vena cava (iv). The delay from injection to the increase in ventilation (TVE) was significantly shorter following ia (1.5 s) compared to iv injections (about 5 s). The delay to the increase in heart rate (THR) was significantly shorter after iv (about 4.5 s) than after ia injections (12.5 s). When isoproterenol and NaCN injections were compared, there was no difference in TVE. Following carotid body resection, the VE response to isoproterenol was greatly reduced after iv and ia injections; however, THR was unaffected. In intact animals breathing 100% O2 the VE response to isoproterenol was significantly reduced with no change in TVE or in the heart rate response. We conclude that the ventilatory increase following the injection of isoproterenol is due primarily to direct stimulation of the carotid bodies.

Semiautomatic blood pressure monitor utilizing an electronic sphygmomanometer.

A semicontinuous but noninvasive blood pressure monitoring system is described. It consists of a commercial electronic sphygmomanometer which utilizes a microphone under an occluding arm cuff to detect the Korotkoff sounds, a pressure transducer, and a simple gating circuit. The gate passes the cuff pressure signal to a recorder only when a proper Korotkoff sound is detected. The cuff is rapidly inflated to just above the anticipated systolic pressure, then deflated at a steady rate of 2-6 Torr/heartbeat. When diastolic pressure is passed, the cuff is fully deflated momentarily before repeating the cycle. Systolic and diastolic pressures can be recorded up to 3 or 4 times/min. Spurious signals are rejected by the electronics which process the output of the microphone. This allows the use of the system in experiments on exercising man and in environments where unwanted signals exist. The system offers greater versatility than commercial semiautomatic pressure monitors, at less than half the cost.