Overview of pulse actions in the human

Obesity and chronic stress are able to desynchronize the temporal pattern of serum levels of leptin and triglycerides

Disruption of the circadian system can lead to metabolic dysfunction as a response to environmental alterations. This study assessed the effects of the association between obesity and chronic stress on the temporal pattern of serum levels of adipogenic markers and corticosterone in rats. We evaluated weekly weight, delta weight, Lee index, and weight fractions of adipose tissue (mesenteric, MAT; subcutaneous, SAT; and pericardial, PAT) to control for hypercaloric diet-induced obesity model efficacy. Wistar rats were divided into four groups: standard chow (C), hypercaloric diet (HD), stress plus standard chow (S), and stress plus hypercaloric diet (SHD), and analyzed at three time points: ZT0, ZT12, and ZT18. Stressed animals were subjected to chronic stress for 1h per day, 5 days per week, during 80 days. The chronic exposure to a hypercaloric diet was an effective model for the induction of obesity and metabolic syndrome, increasing delta weight, Lee index, weight fractions of adipose tissue, and triglycerides and leptin levels. We confirmed the presence of a temporal pattern in the release of triglycerides, corticosterone, leptin, and adiponectin in naïve animals. Chronic stress reduced delta weight, MAT weight, and levels of triglycerides, total cholesterol, and leptin. There were interactions between chronic stress and obesity and serum total cholesterol levels, between time points and obesity and adiponectin and corticosterone levels, and between time points and chronic stress and serum leptin levels. In conclusion, both parameters were able to desynchronize the temporal pattern of leptin and triglyceride release, which could contribute to the development of metabolic diseases such as obesity and metabolic syndrome.

Analysis of the impact of intravenous LH pulses versus continuous LH infusion on testosterone secretion during GnRH-receptor blockade

Gonadotrophin-releasing hormone (GnRH) pulsatility is required for optimal luteinizing hormone (LH) secretion, but whether LH pulsatility is required for physiological testosterone (T) secretion is not known. To test the postulate that pulses of recombinant human (rh) LH stimulate greater T secretion than continuous infusion of the same dose, a potent selective GnRH antagonist was administered overnight to 19 healthy men ages 18-49 yr. Subjects then received saline or rhLH intravenously continuously or as 6-min pulses intravenously every 1 or 2 h at the same total dose. Blood was sampled every 10 min for 10 h to quantify T responses. For the four interventions, the descending rank order of mean LH and mean T concentrations was 1-h = 2-h rhLH pulses > continuous rhLH > saline (P < 10(-3)). Plateau LH and T concentrations correlated positively (R(2) = 0.943, P = 0.029) as did LH concentrations and LH half-lives (R(2) = 0.962, P = 0.019). Percentage pulsatile T secretion assessed by deconvolution analysis (Keenan DM, Takahashi PY, Liu PY, Roebuck PD, Nehra AX, Iranmanesh A, Veldhuis JD. Endocrinology 147: 2817-2828, 2006) was the highest (P = 0.019), and half-time to attain peak T concentrations was the shortest (P < 10(-6)), for 1-h rhLH pulses. Approximate entropy (a pattern-regularity measure) revealed more orderly T secretion for 1- than 2-h rhLH pulses (P = 0.0076). Accordingly, a pulsatile LH signal, while not obligatory to maintain mean T concentrations, controls the mean plasma LH concentration and determines quantifiable patterns of T secretion. These data introduce the question whether blood T patterns in turn supervise distinctive target-tissue responses.

Endocrine responses to upper- and lower-limb resistance exercises with blood flow restriction

To compare endocrine responses to low-intensity resistance exercise with blood flow restriction (BFR) for upperlimb (UL) and lower-limb (LL) muscles, we measured blood lactate, plasma noradrenaline, and serum growth hormone (GH), testosterone, cortisol and insulin-like growth factor-I (IGF-I) before and after the UL (biceps curl and triceps press down) and LL (leg extension and leg curl) exercises with BFR in nine men (26.3 +/- 3.1 yr). The load of 30% of one-repetition maximum (1RM) was used in all the exercises, in which the first set of 30 repetitions was followed by the second and third sets to failure. In each exercise program, the proximal portions of their upper arms (UL) or thighs (LL) were compressed bilaterally by elastic belts. Both the UL and LL caused significant increases in lactate, noradrenaline, GH, testosterone, cortisol, and IGF-I concentrations when compared to the pre-exercise values. A significant difference between the UL and LL was observed only in the area under the curve (AUC) of serum GH concentration, indicating that the LL induced greater GH response than did the UL. The greater GH secretion following the LL may be more advantageous for muscle hypertrophy induced by a long-term training period.

Clinical implications of pulsatile hormone signals

In all biological systems, the information content of hormonal signals is conveyed by the modalities of pulsatile hormone secretion. New mathematical tools for the analysis of pulsatile behaviour and increasing knowledge of the sources of signal variability have enabled us to recognize altered hormonal pulsatility associated with human disease. Its consequences for our understanding of disease mechanisms, for diagnostic procedures and for therapeutic decisions are discussed at the level of single hormones. Increased disorderliness of hormone secretion is a hallmark of pituitary adenomas, indicating functional subsystem autonomy. The effects on target tissues of changing growth hormone therapy from low-frequency administration to long-acting preparations are still incompletely understood. In contrast, the gonadotropic axis is a paradigm for the successful therapeutic use of induced pulsatility changes, where therapy with long-acting gonadotropin-releasing hormone (GnRH) agonists suppresses endogenous gonadotropin pulses and gonadal function, and pulsatile GnRH administration is used to restore normal gonadal function. Future development of endocrine therapies will depend on our knowledge of hormonal pulsatility.