A central question in adenohypophyseal cell physiology concerns the role of transmembrane ionic fluxes in the initiation of the hormone secretion process. In the current report, we investigated the effects of the growth hormone (GH) secretagogues ghrelin and GH-releasing peptide-6 (GHRP-6) on the regulation of the functional expression of voltage-gated Na⁺ channels using the tumoral somatotrope GC cell line as a model. Cells were cultured under control conditions or in presence of the GH secretagogues (GHS) for 96 h, and Na⁺ currents ( I_Na) were characterized in whole cell patch-clamp experiments. GHS treatment significantly increased I_Na density in a dose-dependent manner. The effects of GHRP-6 were accompanied by an augment in conductance without changes in the kinetics and the voltage dependence of the currents, suggesting an increase in the number of channels in the cell membrane. Sustained inhibition of L-type Ca²⁺ channel activity decreased I_Na density and prevented the effects of the GHS, whereas long-term exposure to an L-channel agonist increased I_Na density and enhanced the actions of GHRP-6, indicating that Ca²⁺ entry through these channels plays a role in the regulation of Na⁺ channel expression. Likewise, GHRP-6 failed to enhance Na⁺ channel expression in the presence of membrane-permeable inhibitors of protein kinases A and C, as well as the Ca²⁺/calmodulin-dependent kinase II. Conversely, treatment with a cAMP analog or a protein kinase C activator enhanced both basal and GHS-induced secretion of GH measured by enzyme-linked immunoassay, suggesting that GHRP-6 acting through the ghrelin receptor and different signaling pathways enhances Na⁺ channel membrane expression, which favors hormone release from GC somatotropes.

Objetivo. Caracterizar el sistema de producción bovino doble propósito (SPDP) en unidades de producción pecuaria (UPP) de municipios de la Huasteca Alta Veracruzana (HAV) y determinar la tipología de las UPP dentro del SPDP. Materiales y métodos. Con variables sociales (productor), cuantitativas del hato e índices tecnológicos, agrupados en áreas zootécnicas (Reproducción, Salud, Nutrición, Pastos y Administrativa) se analizó la información de 135 UPP del SPDP recabada a través de encuestas y visitas in situ, con registros de sus actividades sociales, económicas y pecuarias; asi mismo, se analizó el panorama climatológico con información de estaciones meteorológicas de la región. Se utilizó el análisis multivariados K-means y Conglomerado (Statistica V10); con ello, se logró identificar cinco grupos de UPP catalogándose como: Empresarial (n= 4), Transición (n= 29), Tradicional Alto (n=34), Medio (n= 37) y Bajo (n= 31). Con ANDEVA de una vía fueron analizadas las variables socioeconómicas, productivas y propias del hato. Resultados. Las UPP Empresarial y Transición se diferenciaron (p < 0.05) de las de tipo Tradicional por poseer una mayor superficie (hectáreas) utilizada para la ganadería, número de vacas y mayores índices tecnológicos de salud, nutrición y económico (p< 0.05), características que describen la obtención de mayores ingresos por venta la de leche y becerros para la engorda. Conclusiones. El índice tecnológico del SPDP es de 0.37 ± 0.01 a 0.61 ± 0.06 (bajo-medio), esta situación y las condiciones climatológicas actuales afectan su productividad.

In Veracruz, raising livestock takes place in an environment that offers little comfort, and this condition has worsened since 1990. Projections of climate change scenarios for Veracruz, Mexico, show increases in temperature; central Veracruz will be the most affected. Analysis of daily temperatures (ºC) and relative humidity (%) for the period 1917–2016 was carried out to obtain the Livestock Weather Security Index (LWSI) using the Temperature and Humidity Index (THI) provided by the forecast center of the Gulf of Mexico and to determine changes in THI. Cattle comfort was obtained with the equation: THI = 1.8 × T + 32-(0.55–0.55 × HR) × (1.8 × T-26); Where “T” is temperature (°C) and “RH” relative humidity (%). THI values were interpreted as ≤ 74 Comfort, 75–78 Alert, 79–83 Dangerous and ≥ 84 Emergency. Periods of 30 years known as Normal I: (1917–1930), II: (1931–1960), III: (1961–1990), IV: (1991–2016) were made. THI means in the time periods were (I) 75.15 ± 0.061, (II) 75.80 ± 0.041, (III) 75.55 ± 0.044, and (IV) 76.62 ± 0.049 (p < 0.05). Percentage (%) of days for THI categories in each Normal was (I) 34.15, 46.69, 19.14, 0.0; (II) 30.84, 42.13, 27.01, 0.0; (III) 32.53, 39.67, 27.78, 0.009; (IV) 27.54, 34.10, 38.17, 0.17 for Comfort, Alert, Dangerous and Emergency (p < 0.05). Comfort has been reduced in recent years; increases in the percentage of days with THI > 79 are expected.