Kinetics of gentamicin after intravenous, intramuscular, and intratracheal administration in sheep

Kinetics of gentamicin (2.2 mg/kg of body weight) were investigated in 7 sheep after IV bolus administration. The mean serum concentration profile could be described by a 2-compartment open model with a distribution rate constant (alpha) of 3.112 +/- 1.681 hour-1 [half-life, t1/2(alpha) = 17.22 +/- 8.63 minutes] and an overall elimination rate constant (beta) of 0.485 +/- 0.028 hour-1 [t1/2(beta) - 85.87 +/- 5.03 minutes]. The apparent volume of distribution was somewhat restricted [Vd(area) = 0.194 +/- 0.059 L/Kg], and the total body clearance was 1.559 +/- 0.400 ml/kg/min. Equal dosages of gentamicin (2.2 mg/kg) were also given IM and intratracheally (IT). after IM injection, gentamicin reached peak serum concentration at postinjection minutes (PIM) 45, surpassing concentrations after the IV injection for the remainder of the experiment. The IT injection produced detectable serum concentrations at PIM 5, with a peak concentration at PIM 60. The serum drug concentrations after IT injections remained well below concentrations after IV and IM injections. Radiographic analysis of an IT injection of a gentamicin-tantalum suspension revealed good distribution throughout the trachea and proximal bronchi, with physical clearance of the tantalum occurring after greater than or equal to 10 minutes. Aspiration biopsy of the tracheal wash 6 hours after IT gentamicin injection revealed no cytologic response to gentamicin in 6 of 7 sheep, with the single response that of a purulent exudate.

Effect of hypocalcemia on motility of the ruminant stomach

The sensitivity of ruminal and abomasal contractions to hypocalcemia was evaluated in sheep. Serum diffusible calcium concentrations were determined during induction of hypocalcemia (IV infusion of Na2EDTA) and recovery from hypocalcemia (no infusion). Contractile strength of the rumen gradually decreased as serum diffusible calcium concentrations decreased; significant correlation (r = 0.75; P less than 0.001) was observed. Ruminal contractions disappeared before clinical signs of hypocalcemia were seen. Abomasal contractions were slightly reduced when serum diffusible calcium concentrations were equal to those producing ruminal stasis and clinical signs of hypocalcemia. These observations indicated that ruminal dysfunction may occur considerably before the onset of clinical signs of hypocalcemia.

Determination of blood pressure by indirect methods in dogs given acetylpromazine maleate

This study was designed to monitor and compare indirect blood pressures by two methods (ultrasonic Doppler and photoelectric) after intravenous acetylpromazine maleate at three different doses (0.11, 0.55, and 1.10 mg/kg). Sixteen unanesthetized dogs were placed in right lateral recumbency and pressures estimated from the left hind leg at two preinjection times and at 3, 15, 60 and 120 minutes postinjection. This procedure was followed for each dog for each of the three doses. Preinjection ultrasonic mean values and standard deviations were similar to published values. Photoelectric systolic pressures were lower and diastolic pressures higher than ultrasonic systolic and diastolic pressures. The decrease in blood pressure was detected by both methods. Neither method revealed a dose related response.

Functional effects of lesion-induced plasticity: long term potentiation in formal and lesion-induced temporodentate connections

The crossed temporodentate pathway from the entorhinal cortex of one hemisphere which proliferates in response to a contralateral entorhinal lesion in adult rats was analyzed for its ability to exhibit long term potentiation of synaptic efficacy similar to that which occurs in the normal ipsilateral temporodentate pathway. It was found that while the small synaptic response evoked by contralateral entorhinal cortical stimulation in normal rats does not undergo long term potentiation, after unilateral entorhinal lesions and proliferation of the crossed temporodentate pathway, the crossed pathway acquires a capacity for potentiation of synaptic action which qualitatively resembles that of the normal ipsilateral temporodentate circuit. However, despite the potentiation of synaptic drive, no long term enhancement of cell discharge was observed in the re-innervated dentate gyrus even through potentiation of this parameter was very prominent in the ipsilateral pathway. Mechanisms are discussed by which a previously non-potentiating pathway may acquire, as a consequence of lesion-induced sprouting, an ability to undergo long term potentiation of synaptic efficacy in a fasion similar to the ablated pathway. Reasons for the failure to observe potentiation of cell firing are also considered.

Endotoxin absorption in hay-fed and lactic acidotic sheep

Absorption of endotoxin from the gastrointestinal tract was evaluated in hay-fed and lactic acidotic sheep duodenally infused with 10 mg of Escherichia coli endotoxin, and in lactic acidotic sheep not infused. The effect of abomasal fluid on biological activity of endotoxin was also evaluated. Leukopenia was the criterion used for detecting endotoxemia. Absorption of endotoxin from the gastrointestinal tract was not detected in either hay-fed or lactic acidotic sheep. Endotoxin appeared to maintain its activity after incubation with abomasal fluid, and the presence of endogenous endotoxin in abomasal contents was indicated. The results indicate that endotoxin of alimentary origin may not be involved in the lactic acidosis syndrome in ruminants.

Polysynaptic activation of the dentate gyrus of the hippocampal formation: an olfactory input via the lateral entorhinal cortex

The possibility that olfactory input is transmitted to specific subregions of the hippocampal formation via the entorhinal cortex was investigated electrophysiologically by analyzing the laminar profiles of potentials evoked in the hippocampal formation by stimulation of the lateral olfactory tract (LOT). LOT stimulation resulted in long latency (14--20 ms) evoked responses in the dentate gyrus of the hippocampal formation ipsilateral to the stimulation. The variable long latency of these responses and their inability to follow stimulus rates of 40/s suggested that these potentials reflected polysynaptic activation. Analysis of the laminar profiles of the evoked potentials indicated that the responses originated from a synaptic field localized in the outer portion of the stratum moleculare of the dentate gyrus, a terminal distribution which overlaps that of the lateral entorhinal cortical (LEC) projection to the dentate gyrus. Lesions of the LEC eliminated the long latency responses in the dentate gyrus evoked by LOT stimulation. In addition, a conditioning pulse delivered either to the LOT or to the LEC produced paired pulse potentiation of the response elicited by subsequent stimulation of the other structure. No evidence was found to indicate that responses were generated in regio superior of the hippocampus proper following LOT stimulation. Taken together, these results suggest that stimulation of the LOT activates the dentate gyrus of the hippocampal formation by multisynaptic pathways which relay through the lateral portion of the entorhinal area. This finding is discussed with regard to entorhinal cortical organization and the known olfactory projections to the LEC.

Studies of mechanisms of action of secretin and pancreozymin on rumen motility

Rapid intravenous administration of a single bolus of secretin caused a marked decrease in both amplitude and frequency of rumen contractions, whereas pancreozymin administration caused a decrease in frequency but an increase in amplitude of rumen contractions. Alpha receptor blockade with phenoxybenzamine or beta receptor blockade with propranolol did not alter secretin or pancreozymin effects on rumen motility. Blockade of histamine receptor sites with tripelennamine did not prevent the secretin-induced decrease of rumen motility. A marked similarity in the decreased rumen motility pattern was observed when secretin effects were compared to aminophylline effects.