RESUMEN
Coliform mastitis that presents itself at parturition or in the early weeks of bovine lactation is often characterized by severe inflammation and impaired milk production and can lead to death of the animal. Chronic intramammary infections caused by persistent strains of Escherichia coli may result in high production losses. The aim of this study was to determine the inflammatory response to a teat-canal challenge of bovine mammary glands with a persistent strain of E. coli during late gestation (dry period) and into early lactation. Two weeks before parturition, animals were challenged in 2 quarters with 30 cfu of a persistent strain of E. coli; control quarters were vehicle-infused and not infused, respectively. Samples of dry cow secretions were taken from all quarters before challenge and at 6, 12, 18, 24, 48, 72, 96, and 120 h following challenge. Colostrum samples and milk samples were taken from all quarters at parturition and 6, 12, 18, 24, 48, 72, 96 and 120 h postpartum. Bacterial culture, combined with random amplified polymorphic DNA genetic strain-typing analysis, indicated recovery of the bacterial challenge strain until 48 to 96 h postchallenge, and again at parturition and up to 6 and 12h postpartum. One animal exhibited clinical mastitis and the bacterial challenge strain was evident to at least 12 d postpartum. During twice-daily milkings, production levels were lower in bacteria-challenged quarters compared with controls. Somatic cell counts decreased to normal levels at a slower rate in challenged quarters compared with control quarters. Cytokine analysis indicated a minimal proinflammatory cytokine response, including interleukin-1ß and tumor necrosis factor-α in challenged-quarter dry cow samples up to 120 h postchallenge. Interleukin-10 levels were significantly increased by 12h postchallenge in secretions from challenged and control quarters. These preliminary results in 2 cows indicate that proinflammatory signaling after intramammary bacterial infection may be actively suppressed during late gestation. We hypothesize that this immune-inhibitory response allows intramammary infections to become persistent in the dry period and cause clinical signs immediately after parturition.
Asunto(s)
Infecciones por Escherichia coli/veterinaria , Mastitis Bovina/inmunología , Complicaciones Infecciosas del Embarazo/veterinaria , Animales , Bovinos , Recuento de Células/veterinaria , Calostro/química , Calostro/microbiología , Escherichia coli/genética , Escherichia coli/inmunología , Infecciones por Escherichia coli/inmunología , Femenino , Interleucina-1beta/análisis , Glándulas Mamarias Animales/inmunología , Glándulas Mamarias Animales/microbiología , Mastitis Bovina/microbiología , Leche/química , Leche/citología , Leche/microbiología , Embarazo , Complicaciones Infecciosas del Embarazo/inmunología , Complicaciones Infecciosas del Embarazo/microbiología , Técnica del ADN Polimorfo Amplificado Aleatorio/veterinaria , Factor de Necrosis Tumoral alfa/análisisRESUMEN
This study tests the hypothesis that conscious rabbits late in pregnancy (P), but not at midgestation (MP), are less able to maintain arterial pressure during hemorrhage. Blood volume (BV) was elevated (P < 0.05) by an average of 13 +/- 4 (MP) and 35 +/- 3% (P). Rabbits were bled in both the nonpregnant (NP) and P state at 2% of the initial BV per minute. The hemorrhage was stopped after arterial pressure decreased. In NP rabbits, arterial pressure was well maintained near control pressures of 70 +/- 2 mmHg until 38 +/- 2% of the initial BV was removed and then rapidly fell to reach a nadir at 35 +/- 2 mmHg. In contrast, in P rabbits, basal arterial pressure was lower (61 +/- 2 mmHg; P < 0.05) and gradually decreased to below control after <25% of the initial BV was removed. Moreover, the rapid hypotensive phase was triggered with a lower percent BV removal (33 +/- 2%; P < 0.05). Basal heart rate was higher during P (149 +/- 5 vs. 189 +/- 9 beats/min; P < 0.05), and reflex increases were delayed. The slope of the relationship between arterial pressure and vasopressin was not modified during P, although the line was shifted to a lower pressure (P < 0.05). Larger increases in plasma renin activity and ANG II concentration were produced during hemorrhage in P rabbits. In contrast, no differences in the changes in arterial pressure, heart rate, and vasopressin were found between NP and MP rabbits during hemorrhage, although increases in renin and ANG II were greater at MP (P < 0.05). In summary, although P conscious rabbits are less able to maintain blood pressure during hemorrhage, this change is not evident at MP. These data suggest that the factors that mediate the P-induced alterations in arterial pressure regulation are not operative until late in gestation.
Asunto(s)
Angiotensina II/sangre , Hemodinámica/fisiología , Hemorragia/fisiopatología , Complicaciones del Embarazo/fisiopatología , Vasopresinas/metabolismo , Animales , Barorreflejo , Presión Sanguínea , Volumen Sanguíneo , Femenino , Frecuencia Cardíaca , Hematócrito , Embarazo , Conejos , Renina/sangre , Sistema Renina-Angiotensina , Factores de Tiempo , Vasopresinas/sangreRESUMEN
Experiments were performed in conscious rabbits to investigate when during pregnancy cardiac baroreceptor reflex gain decreases. A decrease in gain was first observed after 3 weeks of gestation (-34.1 +/- 4.9 to -15.7 +/- 3.1 beats/min/mm Hg, p < 0.05) and became more pronounced after 4 weeks (-30.2 +/- 4.7 to -8.6 +/- 2.9 beats/min/mm Hg, p < 0.05). These results indicate that the attenuation of baroreflex function does not become fully manifest until late in pregnancy.
Asunto(s)
Barorreflejo , Preñez/fisiología , Animales , Presión Sanguínea , Estado de Conciencia , Femenino , Frecuencia Cardíaca , Embarazo , ConejosRESUMEN
1. Pregnancy-induced changes in acute blood pressure regulation are reviewed. 2. Pregnant animals are less able to maintain arterial pressure during haemorrhage than non-pregnant animals. 3. Baroreceptor reflex-mediated increases in heart rate, renal sympathetic activity, vasopressin, ACTH and cortisol are reduced during pregnancy. Therefore, one explanation for the subnormal ability of pregnant animals to regulate arterial pressure during haemorrhage is that the baroreceptor reflex is not as effective. 4. Chronic increases in oestrogen levels in non-pregnant rabbits do not reduce the gain of baroreflex control of renal sympathetic activity. This and other findings suggest that oestrogen alone does not mediate the blunted baroreflex activity observed during pregnancy.