SUMMARY We studied the effects of caffeine on calcium transport by subcellular organelles isolated from rabbit myocardium. Caffeine increased myofibrillar basic and calcium-activated ATPase activity at 20 mil but not at lower concentrations. Mitochondrial and sarcoplasmic reticulum (SR) calcium accumulation was measured both by dual wavelength spectrophotometry with the calcium-sensitive dye, murexide, and by Millipore filtration with 45 Ca. In mitochondria, caffeine impaired phosphateassisted calcium transport but did not alter the closely related parameters of oxygen uptake, P/O ratio (nmol adenosine diphosphate consumed/n ats oxygen consumed, state 3 respiration) or limited calcium loading. In SR, caffeine impaired calcium accumulation. New methods were used to characterize calcium accumulation in the absence of oxalate according to first order reaction kinetics. Caffeine increased the rate constant while decreasing the calcium accumulated. It also increased the associated calcium-activated ATPase activity at low (30 /IM) but not high (240 /JM) external calcium concentration. In the presence of oxalate, caffeine decreased the rate of calcium accumulation, more with low than high calcium concentration. Net efflux of 45 Ca from preloaded SR also was increased by caffeine. The findings indicate that caffeine impairs active calcium accumulation by making SR vesicle membranes more permeable to calcium.CAFFEINE is useful to demonstrate the role of the sarcoplasmic reticulum (SR) in excitation-contraction coupling in skeletal muscle.

Two experiments were conducted to evaluate the effects of applied heat (greater than or equal to 28 C) and crowding (less than or equal to .9 m2 floor space/animal) stress for 50 days during mid-gestation on glucocorticoid concentrations, corticosteroid binding globulin (CBG) characteristics and reproductive performance of 20 sows (Exp. 1) and 23 gilts (Exp. 2). Blood as collected via puncture of the anterior vena cava on days -1 and 0 before initiation of treatment and on days 1, 2, 12, 13, 48, 29 and 1, 5, 9 +/- l, 19 +/- 1, 50, 63 +/- 3, 90 +/- 1 after initiation of treatment for sows and gilts. respectively. Plasma glucocorticoids and CBG characteristics were determined by competitive protein binding techniques. Overall mean glucocorticoid concentrations for eight sows and 12 gilts subjected to stress were lower (P less than .05) than those of control animals, CBG binding capacities (CBC) were lower (P less than .05) in treated sows and gilts bled on days 12 and 9 +/- 1 after initiation of stress, respectively. Overall mean CBC and affinity (Ka) of cortisol to bind to the CBG molecule were lowered (P less than .05) in stressed gilts. Other than a reduction (P less than .05) in gestation length observed in stressed crossbred sows, reproductive performance was not affected by stress. When infrequent blood samplings are employed, measurement of CBC may serve as a more precise indicator of a physiological stress response than glucocorticoid concentration.

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Gilts that had previously been fed ad libitum or 75% ad libitum intake and 100 or 150% National Research Council recommended daily Ca and P from weaning to 100 kg were used in a reproductive study in which a 14% protein diet was fed. Foot and leg measurements, subjective toe scores and structural soundness scores were taken at each of three parities, 21 d postweaning. Sows previously ad libitum-fed generally had larger front toes than limit-fed sows; whereas, hind toes were larger for sows previously fed 150% Ca and P levels than sows fed 100% Ca and P. Sows previously fed the ad libitum-150% Ca and P diet had the largest toes. Front inside toes were larger than hind inside toes, but the reverse was observed for front and hind outside toes, with the magnitude of the difference between the inside and outside toes greater for the hind foot. Toe size increased over parities with the greatest increase from parity 2 to 3. Incidence and severity of toe pad and horn scores were generally unaffected by previously fed energy and Ca and P levels and were not correlated to toe size. Hind feet exhibited a larger number of lesions than front feet and outside toes exhibited a larger number of lesions than inside toes, with the hind outside toe exhibiting the greatest number of lesions. In general, incidence and severity of toe lesions decreased or were unchanged from parity 1 to 3. Structural soundness scores were unaffected by previously fed energy or Ca and P levels, but were quadratically affected by parity, with a small increase (poorer) from parity 1 to 2 and a large improvement from parity 2 to 3. Soundness scores were not related to any of the feet or leg measurements and characteristics. Restricting growth rate and feeding elevated Ca and P levels during growth had no effect on incidence and severity of lesions on the toes and overall structural soundness of sows kept for three parities.