Juvenile Female Pigs Research Articles

Biomechanical behavior of scar tissue and uninjured skin in a porcine model

A new method to test axial and transverse tensile properties of skin was developed to improve our understanding of skin mechanical behavior, and how it changes following injury and formation of a scar. Skin tissue was evaluated at 70 days following full-thickness wounding in juvenile female pigs (N=14). Samples were taken in the axial (cranial-caudal) and transverse (dorsal-ventral) directions, for both scar tissue and uninjured skin, and were evaluated mechanically in vitro using a protocol of stress relaxation followed by tensile failure. Uninjured skin was more compliant, with a larger toe-in region, and faster load relaxation, in the axial direction than the transverse. Such directional differences were not present in high-load responses, such as linear stiffness or failure properties. When compared with uninjured skin, scars displayed a similar linear stiffness, with considerably reduced failure properties, and reduced low-load compliance. Scars showed no directional differences in low-load behavior, viscous response, or failure properties. These findings suggest morphological changes that may occur with injury that are consistent with the viscoelastic and directional changes observed experimentally. This improved understanding of how injury affects skin biomechanical function provides valuable information necessary for the design of successful grafting procedures and tissue-engineered skin replacements.

121 Laser Speckle Perfusion Imaging of Wound Healing in a Porcine Model

A Laser Speckle Perfusion Imaging (LSPI) system has been developed to achieve rapid, high-resolution, noninvasive imaging of tissue blood flow. This study was designed to evaluate LSPI for monitoring dermal blood flow during the wound healing process in a well-established porcine model. Full-thickness excisional wounds (2 × 2 cm) were created on the dorsal skin of 11 juvenile female red Duroc pigs. The skin wounds were imaged weekly with the LSPI system until day 49 postwounding. Blood flow values for the wounds were normalized using the values from the surrounding healthy skin to account for variations in systemic perfusion from one scan date to the next. An average normalized perfusion value was obtained from the scans of all animals for each time point. Wound perfusion at the time of reepithelialization reached ∼165% of the surrounding skin (p < 0.001). This elevation in wound perfusion slowly and steadily decreased over time, until day 49 postwounding, at which time the values returned to normal. This trend toward decreased wound perfusion over time has previously been reported in human burn wounds using the LSPI instrument. Further, the LSPI data from this study and from other human studies correlates well with data generated using the more widely established Laser Doppler Imaging (LDI) technique. The faster scan time and higher resolution of the LSPI method provides a distinct clinical advantage, both in terms of patient comfort and for reliably matching perfusion characteristics to their associated anatomical features. The fast temporal response of the LSPI instrument could be used to monitor vascular responses to mechanical or pharmacological interventions to study dynamic vascular changes to damaged tissues. This study validates LSPI as a tool to measure blood flow in skin wounds and further supports the use of the juvenile female pig as a model of excisional wound healing, yielding results comparable to healing in humans. Acknowledgments: Funding provided by CIHR, AHFMR, and NSERC

005 The Biomechanical Behavior of Scar Tissue and Uninjured Skin in a Porcine Model

To investigate changes in the mechanical properties of skin with injury, tissue was evaluated 70 days following full thickness wounding in juvenile female Yorkshire pigs (N = 14). Samples were taken in the axial (cranial-caudal) and transverse (dorsal-ventral) directions, for both scar tissue and uninjured skin. The samples were evaluated mechanically in vitro using a protocol of stress relaxation followed by tensile failure, in an INSTRON universal test machine. Specimens were subjected to a 10% elongation and held for a 4-min isometric period, after which they were returned to the original length and failed in tension. Axial normal skin exhibited a smaller force at 10% elongation (−58%, p = 0.002), and higher failure load (p = 0.027) and displacement (p = 0.028) than transverse. Scarring reduced the failure strength on average by 60% in the axial and 65% in the transverse directions (p < 0.001), with large decreases (>50%) in displacement at failure in both directions (p < 0.001). Elongation of 10% produced a larger force in axial scars (p < 0.001) than their normal counterparts, indicating a reduction in small-displacement compliance. Axial scars exhibited greater failure strength (p = 0.009) than transverse scars, yet no significant differences were observed in elongation to failure or load at 10% elongation. These results indicate that normal skin exhibits higher compliance and failure strength in the axial direction. Following injury, the strength and compliance of the tissue are greatly reduced, and the strong compliance directionality originally observed, is lost. Therefore it appears that the healing response leads to increases in tissue stiffness, such that small displacements result in larger tissue loads. This is further complicated by the reduced ability of the scar to resist failure. Taken together, these findings illustrate the compounding negative effects of scar on tissue integrity and function. Acknowledgments: Alberta Ingenuity Fund, CIHR and NSERC

In vivo measurement of nicotinic acetylcholine receptors with [18F]norchloro‐fluoro‐homoepibatidine

Functional changes of nicotinic acetylcholine receptors (nAChR) are important during age-related neuronal degeneration. Recent studies demonstrate the applicability of the nAChR ligand 2-[(18)F]F-A-85380 for neuroimaging of patients with dementias. However, its binding kinetics demands a 7-h acquisition time limiting its practicality for clinical PET studies. Thus, the authors developed [(18)F]norchloro-fluoro-homoepibatidine ([(18)F]NCFHEB) for nAChR imaging. The kinetics of the two enantiomers of [(18)F]NCFHEB were compared with 2-[(18)F]F-A85380 in porcine brain to evaluate their potential for human neuroimaging. Twenty-four juvenile female pigs were studied with PET using [(18)F]NCFHEB. Nine animals received an additional i.v. injection (1 mg/kg) of the nAChR agonist A81418 before radiotracer administration followed by infusion (2 mg/kg/7h) thereafter. Several compartment models were applied for quantification. (-)- and (+)-[(18)F]NCFHEB showed a twofold to threefold higher brain uptake than 2-[(18)F]F-A-85380. All three radiotracers displayed spatially heterogeneous binding kinetics in regions with high, moderate, or low specific binding. The equilibrium of specific binding of (-)-[(18)F]NCFHEB was reached earlier than that of (+)-[(18)F]NCFHEB or 2-[(18)F]F-A85380. Continuous administration of the nAChR agonist A81418 inhibited the specific binding of (-)- and (+)-[(18)F]NCFHEB but not of 2-[(18)F]F-A85380. The peripheral metabolism of (+)-[(18)F]NCFHEB proceeded somewhat slower than that of the other radiotracers. Both enantiomers of [(18)F]NCFHEB are appropriate radiotracers for neuroimaging of nAChR in pigs. Their binding profile in vivo appears to be more selective than that of 2-[(18)F]F-A85380. (-)-[(18)F]NCFHEB offers a faster equilibrium of specific binding than 2-[(18)F]F-A85380.

The Distribution and Chemical Coding of Intramural Neurons Supplying the Porcine Stomach – the Study on Normal Pigs and on Animals Suffering from Swine Dysentery

The present study was designed to investigate the expression of biologically active substances by intramural neurons supplying the stomach in normal (control) pigs and in pigs suffering from dysentery. Eight juvenile female pigs were used. Both dysenteric (n = 4; inoculated with Brachyspira hyodysenteriae) and control (n = 4) animals were deeply anaesthetized, transcardially perfused with buffered paraformalehyde, and tissue samples comprising all layers of the wall of the ventricular fundus were collected. The cryostat sections were processed for double-labelling immunofluorescence to study the distribution of the intramural nerve structures (visualized with antibodies against protein gene-product 9.5) and their chemical coding using antibodies against vesicular acetylcholine (ACh) transporter (VAChT), nitric oxide synthase (NOS), galanin (GAL), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), Leu(5)-enkephalin (LENK), substance P (SP) and calcitonin gene-related peptide (CGRP). In both inner and outer submucosal plexuses of the control pigs, the majority of neurons were SP (55% and 58%, respectively)- or VAChT (54%)-positive. Many neurons stained also for CGRP (43 and 45%) or GAL (20% and 18%) and solitary perikarya were NOS-, SOM- or VIP-positive. The myenteric plexus neurons stained for NOS (20%), VAChT (15%), GAL (10%), VIP (7%), SP (6%) or CGRP (solitary neurons), but they were SOM-negative. No intramural neurons immunoreactive to LENK were found. The most remarkable difference in the chemical coding of enteric neurons between the control and dysenteric pigs was a very increased number of GAL- and VAChT-positive nerve cells (up to 61% and 85%, respectively) in submucosal plexuses of the infected animals. The present results suggest that GAL and ACh have a specific role in local neural circuits of the inflamed porcine stomach in the course of swine dysentery.

Propofol is Associated with Impaired Brain Metabolism during Hypothermic Circulatory Arrest: An Experimental Microdialysis Study

Propofol is a widely used anesthetic in cardiac surgery. It has been shown to increase cerebrovascular resistance resulting in decreased cerebral blood flow. Efficient brain perfusion and tissue oxygenation during cardiopulmonary bypass (CPB) is essential in surgery requiring hypothermic circulatory arrest (HCA). The effects of propofol on brain metabolism are reported in a surviving porcine model of HCA. Twenty female juvenile pigs undergoing 75 minutes of HCA at a brain temperature of 18 degrees C were assigned to either propofol- or isoflurane anesthesia combined with alpha-stat perfusion strategy during CPB cooling and rewarming. Brain microdialysis analysis was used for determination of brain metabolism, and tissue oxygen partial pressure and intracranial pressures were also followed-up until 8 hours postoperatively. Brain concentrations of glutamate and glycerol were significantly higher in the propofol group throughout the experiment (P < .01 and P < .01, respectively). The lactate/pyruvate ratio was significantly higher in the propofol group at 6-, 7-, and 8-hour intervals (P < .05, P < .01, and P < .05, respectively). The intracranial pressure was significantly higher at the 8-hour postoperative interval (P < .05) in the propofol group. A trend toward higher brain oxygen concentrations was observed in the isoflurane group. Anesthesia with propofol as compared with isoflurane is associated with impaired brain metabolism during experimental HCA.

Genetic analysis of skin wound healing and scarring in a porcine model

ABSTRACTContraction is a normal part of skin wound healing and wound closure; however, excessive contraction and severe scarring concern patients and physicians alike. The present study has investigated the degree and kinetics of wound contraction in a porcine model of wound healing, to elucidate the genetic and molecular basis for abnormal skin wound healing and scarring. Healing of excisional skin wounds in juvenile female Yorkshire pigs closely resembled normal healing in humans. In contrast, identical wounds in female red Duroc pigs contracted significantly more, forming hypercontracted, hyperpigmented scars. Yorkshire × red Duroc F1 animals healed without hyperpigmentation, but with significantly greater wound contraction than observed in either parent breed. To examine the genetic transmission of the hypercontractile phenotype, all F1 animals were bred to a single Yorkshire boar, generating 20 backcross animals. All backcross animals healed with significantly less contraction than the normal Yorkshire animals. These findings suggest that the genetic contribution to scar phenotype in this animal model is complex, with a limited number of major genes controlling wound contraction, and an unknown number of minor genes that appear to modulate the impact of the major genes.

Dietary reversal of experimental hypercholesterolemia improves endothelial dysfunction of epicardial arteries but not of small coronary vessels in pigs

Endothelial dysfunction is characterized by impaired vasodilation, increase of oxidative stress and inflammation. The current study was designed to test the hypothesis that reversal of hypercholesterolemic diet alone does not normalize all the parameters of endothelial dysfunction. After 10 weeks on a high-cholesterol diet, female juvenile pigs were randomized to normal diet ( n = 5, “Reversals”) or continued on the same diet ( n = 6, “HC”) for another 6 weeks. A control group of 11 pigs received a normal diet (“C”). Coronary epicardial and arteriolar endothelial function was tested in vitro. NFκB and p47phox expression was analyzed in epicardial arteries and myocardium, respectively. P47phox localization in coronary arteries was demonstrated with immunohistochemistry. Lipid levels normalized in Reversal pigs. Epicardial arteries of Reversals showed a normalized relaxation and NFκB expression compared to HC ( p < 0.05). Small vessel relaxation remained attenuated, and expression of p47phox in myocardial tissue was elevated in Reversals compared to C ( p < 0.05). Dietary lowering of serum cholesterol and LDL improves vascular function of epicardial arteries but neither of small vessels nor vascular oxidative stress within this time frame. Hence, dietary normalization of serum lipid levels alone may not be synonymous to normalization of the components of endothelial dysfunction.

The Distribution and Chemical Coding of Intramural Nerve Structures Supplying the Porcine Stomach

The present study investigated the arrangement and chemical coding of intramural nerve structures supplying the porcine stomach. Tissue samples comprising all layers of the wall of the ventricular fundus were collected from juvenile female pigs (n = 4), which were first deeply anaesthetized and then transcardially perfused with buffered paraformaldehyde. The cryostat sections were processed for double‐labelling immunofluorescence to study the distribution of the intramural nerve structures (visualized with antibodies against protein gene‐product 9.5) and their neurochemical characteristics using antibodies against vesicular acetylcholine transporter (VAChT), nitric oxide synthase (NOS), galanin (GAL), vasoactive intestinal‐polypeptide (VIP), somatostatin (SOM) and substance P (SP). The study confirmed the presence of three distinct nerve plexuses within the wall of the porcine stomach including one myenteric plexus and two, outer and inner, submucous plexuses. The outer and inner submucous plexuses (OSP and ISP, respectively) were similar in respect to the chemical coding of neurons they contained. Most of the neurons expressed immunoreactivity to SP (ISP 58%; OSP 60%) or to VAChT (ISP 56%; OSP 56%), some of them stained for GAL (ISP 18%; OSP 15%) and solitary nerve cells were SOM‐positive (in ISP only). No neurons in the submucous plexuses displayed immunoreactivity to VIP or NOS. In the myenteric plexus, some neurons stained for NOS (20%), VAChT (15%), GAL (10%), VIP (8%) or SP (8%) while no neurons immunoreactive for SOM were encountered. In both submucous and myenteric plexuses, many varicose nerve fibres expressed immunoreactivity to VAChT, GAL or SP, while VIP‐, SOM‐ or NOS‐positive nerve terminals were less numerous. The comparison of the present results with those obtained by other authors has revealed distinct inter‐species differences regarding the arrangement and chemical coding of nerve structures supplying the mammalian stomach.

PH-Stat Versus α-Stat Acid–Base Management Strategy During Hypothermic Circulatory Arrest Combined With Embolic Brain Injury

There is some evidence of beneficial metabolic effects associated with the pH-stat than with alpha-stat perfusion strategy, but this is tempered by a likely increased risk of embolism to the brain, especially in adult patients. We investigated this possible adverse effect in an experimental model that combined hypothermic circulatory arrest (HCA) and embolic brain injury. Twenty-four female juvenile pigs undergoing 25 minutes of HCA at a brain temperature of 18 degrees C were assigned to either alpha-stat (n = 12) or pH-stat (n = 12) strategy during cardiopulmonary bypass. Before the initiation of HCA, the descending aorta was clamped and 200 mg of albumin-coated polystyrene microspheres (250 to 750 microm in diameter) were injected into the isolated aortic arch in both groups. The 7-day survival rate was 75% in the pH-stat group and 50% in the alpha-stat group (p = 0.40). The pH-stat group had significantly better behavioral scores on postoperative days 5 (p = 0.03) and 6 (p = 0.04). The pH-stat strategy was associated with better postoperative intracranial pressures and histopathologic scores, but such differences did not reach statistical significance. The alpha-stat group had lower brain glucose concentrations postoperatively as well as higher brain lactate/glucose and lactate/pyruvate ratios These results suggest that pH-stat strategy does not cause any worse brain injury than the alpha-stat strategy. Indeed, the pH-stat strategy is associated with a slightly better outcome compared with the alpha-stat strategy, even in the setting of cerebral embolization. This observation suggests that the pH-stat strategy could also be used in adults during deep hypothermic cardiopulmonary bypass despite the increased risk of intraoperative cerebral embolization.

Foraging behaviour in domestic pigs (Sus scrofa): remembering and prioritizing food sites of different value

This experiment investigated whether domestic pigs can remember the locations of food sites of different relative value, and how a restricted retrieval choice affects their foraging behaviour. Nine juvenile female pigs were trained to relocate two food sites out of a possible eight in a spatial memory task. The two baited sites contained different amounts of food and an obstacle was added to the smaller amount to increase handling time. On each trial, a pig searched for the two baited sites (search visit). Once it had found and eaten the bait, it returned for a second (relocation) visit, in which the two same sites were baited. Baited sites were changed between trials. All subjects learnt the task. When allowed to retrieve both baits, the subjects showed no preference for retrieving a particular one first (experiment 1). When they were allowed to retrieve only one bait, a significant overall preference for retrieving the larger amount emerged across subjects (experiment 2). To test whether this preference reflected an avoidance of the obstacle with the smaller bait, 15 choice-restricted control trials were conducted. In control trials obstacles were present with both baits. Pigs continued to retrieve the larger bait, indicating they had discriminated between the two food sites on the basis of quantity or profitability and adjusted their behaviour accordingly when the relocation choice was restricted. This suggests for the first time that domestic pigs have the ability to discriminate between food sites of different relative value and to remember their respective locations.

Effect of puberty on coronary arteries from female pigs.

Vascular function changes following loss of ovarian hormones in women at menopause and in experimental animals following surgical ovariectomy. Little is known about changes in vascular function during hormonal transition from sexual immaturity (juvenile) to sexual maturity. Therefore, experiments were designed to determine effects of natural puberty on vascular function in female pigs. Tissue was studied from eight juvenile (2-3 mo) and eight adult (5-6 mo) female pigs. Plasma nitric oxide (NO) was measured, and mRNA for endothelium-derived NO synthase (eNOS) and eNOS protein were determined in aortic endothelial cells. Rings of coronary arteries were suspended for measurement of isometric force in organ chambers. Serum 17beta-estradiol levels were comparable in the two groups, whereas the arithmetic mean of progesterone levels was about two-thirds lower in adults compared with juvenile pigs. Plasma NO was significantly higher in juveniles compared with adults, but mRNA and protein for eNOS were comparable. In coronary arteries, an alpha2-adrenergic agonist caused greater endothelium-dependent relaxations in rings from juvenile compared with adult pigs. Relaxations to bradykinin were similar in arteries from both groups, but inhibition of NO reduced relaxations only in arteries from juvenile pigs. Relaxations from NO were greater in arteries from adult compared with juvenile female pigs. In conclusion, coronary arterial endothelial and smooth muscle responses are selectively modulated at puberty in female pigs. At maturity, plasma NO is reduced and sensitivity of the smooth muscle to exogenous NO is increased. Posttranscriptional regulation of eNOS protein may explain differences in NO bioavailability in juvenile pigs.

Inhaled budesonide in experimental chlorine gas lung injury: influence of time interval between injury and treatment.

To examine the time window between injury and treatment during which nebulized corticosteroid lessens lung injury induced by chlorine gas inhalation. An experimental laboratory study. Academic research laboratory. Twenty-four juvenile female pigs. Twenty-four mechanically ventilated pigs were exposed to chlorine gas (400 PPM in air) for 20 min, then divided into four groups (six in each group). Nebulized budesonide (BUD) was given immediately (BUD 0 min), 30 min (BUD 30 min) or 60 min (BUD 60 min) after chlorine gas exposure. Six pigs receiving nebulized saline served as controls. Hemodynamics, gas exchange and lung mechanics were evaluated for 5 h after chlorine gas exposure. All animals had an immediate increase in airway and pulmonary artery pressure and a sharp drop of arterial oxygenation. The mean arterial oxygen tension of BUD 0 min and BUD 30 min animals was significantly higher than in the control and the BUD 60 min groups ( p<0.001). The recovery of lung compliance in the BUD 0 min and the BUD 30 min groups was significantly more rapid than in the control and the BUD 60 min groups ( p<0.001). The pulmonary wet to dry weight ratio was greater in the control group than in the BUD-treated groups ( p<0.05). Treatment with inhaled budesonide immediately or 30 min after chlorine gas lung injury had similar positive effects on symptoms and signs of pulmonary injury, whereas treatment delayed for 60 min was less effective.

Dietary n-3 fatty acids alter the contractile response to thromboxane A 2 agonists of porcine coronary arteries

Dietary supplementation with marine fish oils rich in n-3 fatty acids reduces circulating thromboxane A 2 (TxA 2). However, the effects on thomboxane A 2 receptor mediated vascular reactivity are uncertain. The aim of this study was to test the hypothesis that dietary modification of TxA 2 levels alters vascular responsiveness to TxA 2 analogues. Juvenile female white pigs were fed a diet enriched in either 5% (w/w) fish oil or beef tallow for 6 weeks. Serum and myocardial tissue levels of eicosapentaenoic and docosahexaenoic acid reached a plateau during this period. Vascular responses were measured in isolated coronary arterial rings with intact endothelium by isometric tension measurement. Arteries from pigs fed fish oil produced a greater maximum vasoconstrictor tension to the TxA 2 analogue U46619 than did rings from pigs fed beef tallow (120 ± 6% compared to 92 ± 8%, values represented as a percentage relative to the maximum vasoconstrictor effect obtained to KCl, regression analysis, analysis of variance, P ≤ 0.05). The vasoconstrictor potency of U46619 was similar in both treatment groups. The vasoconstrictor EC 50 was 10.3 (6.8–15.7) nmol/L (mean, 95% confidence interval) for fish oil and 9.5 (5.7–15.8) nmol/L for beef tallow treated animals. Changes in vascular responses to U46619 were associated with a fourfold difference in plasma thromboxane B 2 levels between treatment groups (12.1 ± 2.6 pg/mL fish oil, 48.3 ± 3.1 pg/mL beef tallow, Students’ unpaired t-test P ≤ 0.05). Vasoconstrictor responses obtained to endothelin-1, KCl and 5-hydroxtryptamine and the vasodilator response to sodium nitroprusside were not different between treatment groups. Dietary manipulation of thromboxane A 2 levels by n-3 fatty acids alters vascular reactivity to U46619, possibly as a result of agonist-induced desensitization of thromboxane A 2 receptors.

The Role of Cerebral Microdialysis in Predicting the Outcome after Experimental Hypothermic Circulatory Arrest

Objective –To evaluate whether and which of the cerebral microdialysis parameters are predictive of postoperative outcome after an experimental 75-min period of hypothermic circulatory arrest (HCA) in a chronic porcine model. Design –Seventy-four juvenile female pigs underwent a 75-min period of HCA at 20°C. A microdialysis catheter was placed into the cortex gray matter and brain extracellular concentrations of glucose, lactate, glycerol and glutamate were measured throughout the experiment by enzymatic methods using a microdialysis analyzer. Surviving animals were sacrificed on the 7th postoperative day and histopathological examination of the brain was performed. Results –Brain glucose concentrations were higher in animals that survived ( p = 0.017), especially from the 90-min until the 7-h interval after the start of rewarming. The blood venous concentrations of glucose were also higher among survivors, and correlated significantly with the brain glucose levels at 2-h and 4-h intervals after the start of rewarming. Higher concentrations of brain lactate, glycerol and glutamate were observed throughout the study among animals that died postoperatively. Brain glutamate and glycerol concentrations were significantly, negatively correlated with brain glucose concentrations. The lactate/glucose ratio was significantly lower among survivors during the postoperative period ( p = 0.014). Furthermore, brain glucose concentrations were higher and brain glycerol concentrations lower among the animals that did not develop brain infarction, but such differences did not reach statistical significance. Conclusion –Cerebral microdialysis is a useful tool for cerebral monitoring during experimental HCA. Low brain glucose concentrations and high brain lactate/glucose ratios after HCA are strong predictors of postoperative death. Brain glucose concentrations are negatively correlated with brain glycerol and glutamate concentrations.

Progesterone-Facilitated Lordosis in Medial Preoptic Area-Lesioned, Juvenile Guinea Pigs

Juvenile female guinea pigs rarely display lordosis in response to estradiol and progesterone treatments that elicit sexual receptivity in adults. To test the hypothesis that the medial preoptic area (MPOA) tonically inhibits the display of steroid-induced lordosis in juveniles, 11-day-old guinea pigs were ovariectomized (OVX) and received bilateral, sham, or electrolytic lesions aimed at the MPOA 3–4 days later. At 20–22 days of age, these females were tested for the expression of sexual receptivity following injections of estradiol benzoate (EB, 10 μg sc) and progesterone (0.5 mg sc, 40 h after EB). The lesions damaged portions of the MPOA, the nucleus of the diagonal band of Broca, the lateral aspect of the medial preoptic nucleus, the medial part of the preventricular portion of the periventricular nucleus, and the anterior commissure. The lesions did not alter the display of estradiol-induced lordosis. However, after treatment with EB plus progesterone, 20% of the sham-lesioned females displayed lordosis, as compared to 80% of the MPOA-lesioned animals. These data are consistent with the hypothesis that neurons originating in and/or traversing the MPOA tonically suppress the display of progesterone-facilitated lordosis in juvenile guinea pigs. Removal of this inhibitory input allows prepubertal females to respond behaviorally to estradiol and progesterone in an adult-typical fashion.

THE EFFECT OF INFRARENAL AORTIC CROSS CLAMPING AND DECLAMPING ON RENAL FUNCTION IN THE PIG

Renal insufficiency following periods of infrarenal aortic cross clamping has been reported by some investigators but not by others, and conflicting views have been expressed concerning the ability of renal autoregulation to overcome the adverse circulatory effects of cross clamping. The object of this study was to examine the blood flow distribution to four layers within the renal cortex (subcapsular to juxtamedullary) and measure global renal function following application and release of an aortic cross clamp after 90 min. Nine juvenile female pigs weighing 25 to 50 kg were anaesthetized and subjected to intensive physiological monitoring. Throughout the study the blood pressure and cardiac output were maintained as close as possible to control levels by fluid administration and varying the depth of anaesthesia. Renal cortical blood flow was estimated by means of radionuclide labelled microspheres and global renal function was determined by the measurement of creatinine clearance. The aortic cross clamp was applied for 90 min immediately distal to the renal arteries and proximal to the inferior mesenteric artery. Cardiovascular and renal parameters were recorded on four occasions during each experiment, prior to, 10 and 60 min after cross clamping, and 30 min after clamp release. No significant changes in cardiac output, systemic blood pressure of global renal function were recorded during the study. There was, however, a significant fall in renal blood flow following release of the aortic cross clamp but this was not associated with any significant redistribution of blood flow within the renal cortex. In the pigs studied, the application of an infrarenal aortic cross clamp did not have any adverse effects on the cardiovascular system or on global renal function.(ABSTRACT TRUNCATED AT 250 WORDS)

Opiate Receptor Blockade Enhances the Display of Progesterone-Facilitated Lordosis in Juvenile Female Guinea Pigs

Juvenile female guinea pigs rarely display estradiol-induced or progesterone-facilitated sexual receptivity. This experiment was designed to test the hypothesis that endogenous opiate peptides tonically inhibit the display of steroid-induced lordosis in juvenile females. Hartley guinea pigs were ovariectomized (OVX) at 10-11 days of age and treated with estradiol benzoate (EB, 10 μg) 5-7 days later. Injection of the opiate antagonist, naloxone (2.0 mg/kg), did not facilitate lordosis (compared to vehicle) in EB-primed, OVX juveniles; when these animals were subsequently given progesterone, and the treatment groups were reversed (i.e., the group previously treated with vehicle received 2.0 mg/kg naloxone 4.5 hr after progesterone, and vice versa), four of six naloxone-injected animals displayed lordosis, compared to one of six control animals. In a second experiment, a range of doses of naloxone was administered to EB-plus progesterone-treated OVX juveniles. Naloxone at the 2.0 mg/kg dose resulted in a significant increase in the percentage of females displaying lordosis, with lower doses (0.5-1.0 mg/kg) producing responses intermediate between those observed in animals receiving the 2.0 mg/kg dose and the vehicle. Furthermore, the facilitatory effect of naloxone on sexual receptivity was completely blocked by concomitant injection of morphine (10.0 mg/kg). These data suggest that endogenous opiates tonically inhibit the display of progesterone-facilitated lordosis in juvenile female guinea pigs.

Further studies on the role of the gonads in determining the ontogeny of gonadotropin secretion in the guinea pig (Cavia porcelus).

To further examine whether nongonadal restraint of gonadotropin secretion during prepubertal development plays a major role in the timing of puberty in the guinea pig, as it does in the monkey and other primates, two experiments were performed. In the first, neonatal male and female guinea pigs were either bilaterally gonadectomized or sham gonadectomized on day 2 of age, or left intact. Circulating LH concentrations were measured in blood samples collected by cardiac puncture every 4 days beginning on day 2 of age and continuing until the animals were 98 days of age. In the second experiment, the time course of the LH response to ovariectomy was examined in juvenile female guinea pigs that were castrated on day 10 of age and were either isolated from or allowed to remain with their mothers for the duration of the study. To place into perspective the time course of the LH response to prepubertal gonadectomy, the effect of castration on LH secretion in adult animals was also examined. Serum LH concentrations were determined by a RIA that employed GDN-15 as the first antibody. Orchidectomy on day 2 of age resulted in an immediate and progressive rise in serum LH concentrations, which plateaued by 30 days of age at levels indistinguishable from those of adult castrates. In contrast, ovariectomy on day 2 of age failed to elicit an immediate rise in serum LH. Instead, circulating LH concentrations in neonatally castrated female guinea pigs were not significantly different from those in intact controls until day 14 of age, at which time serum LH rose progressively to plateau by 30 days of age at levels comparable to those in adult castrates. The time courses of LH secretion after ovariectomy of 10-day-old guinea pigs that were either isolated from or allowed to remain with their mothers were not significantly different and were similar to that observed after ovariectomy at 2 days of age. For reasons presented in detail in Discussion, the foregoing findings fail to support the view that nongonadal restraint of gonadotropin secretion during prepubertal development plays a major role in the timing of sexual maturation in the guinea pig. This laboratory rodent, therefore, may be viewed as a poor paradigm for study of the neuroendocrine basis of puberty in primates.

Development of steroid-induced lordosis in female guinea pigs: Effects of different estradiol and progesterone treatments, clonidine, and early weaning

The ability of developing ovariectomized (OVX) guinea pigs to display lordosis following a variety of steroid treatments which are behaviorally effective in adults was examined. Females OVX at 11 days of age did not display lordosis at 20 days of age, following treatment with several dose combinations of estradiol benzoate (EB, 10–50 μg) and progesterone (0.5–5 mg). By 30 days of age, 25% of the animals responded to EB plus progesterone, and by 40 days of age, adult-typical responses were observed. The developmental profile of responsiveness to steroids was not altered by varying the age at OVX, or by allowing pups to remain with a lactating mother. OVX females given estradiol (E 2) implants did not exhibit progesterone-facilitated lordosis earlier than those treated with EB; however, the former group did show an unusually high incidence of progesterone-independent lordosis at 40 days of age. Twenty-day-old females also did not respond behaviorally to discrete pulses of E 2 followed by progesterone, a treatment which was very effective in adults. Finally, lordosis was not facilitated in EB-primed, 20-day-old females by the α-noradrenergic agonist, clonidine, a treatment which was effective in adult females. These data illustrate a variety of conditions under which juvenile female guinea pigs do not exhibit steroid-induced lordosis. Since 20-day-old, EB-treated females also did not exhibit clonidine-facilitated lordosis, incomplete development of the central steroid-responsive and/or nor-adrenergic systems may contribute to the inability to display steroid-induced estrous behavior at this age.