https://pharmrev.aspetjournals.org/content/pharmrev/46/2/205.full.pdf

International Union of Pharmacology classification of prostanoid receptors: properties, distribution, and structure of the receptors and their subtypes.

Resistance exercise has been shown to elicit a significant acute hormonal response. It appears that this acute response is more critical to tissue growth and remodelling than chronic changes in resting hormonal concentrations, as many studies have not shown a significant change during resistance training despite increases in muscle strength and hypertrophy. Anabolic hormones such as testosterone and the superfamily of growth hormones (GH) have been shown to be elevated during 15-30 minutes of post-resistance exercise providing an adequate stimulus is present. Protocols high in volume, moderate to high in intensity, using short rest intervals and stressing a large muscle mass, tend to produce the greatest acute hormonal elevations (e.g. testosterone, GH and the catabolic hormone cortisol) compared with low-volume, high-intensity protocols using long rest intervals. Other anabolic hormones such as insulin and insulin-like growth factor-1 (IGF-1) are critical to skeletal muscle growth. Insulin is regulated by blood glucose and amino acid levels. However, circulating IGF-1 elevations have been reported following resistance exercise presumably in response to GH-stimulated hepatic secretion. Recent evidence indicates that muscle isoforms of IGF-1 may play a substantial role in tissue remodelling via up-regulation by mechanical signalling (i.e. increased gene expression resulting from stretch and tension to the muscle cytoskeleton leading to greater protein synthesis rates). Acute elevations in catecholamines are critical to optimal force production and energy liberation during resistance exercise. More recent research has shown the importance of acute hormonal elevations and mechanical stimuli for subsequent up- and down-regulation of cytoplasmic steroid receptors needed to mediate the hormonal effects. Other factors such as nutrition, overtraining, detraining and circadian patterns of hormone secretion are critical to examining the hormonal responses and adaptations to resistance training.

Hormonal Responses and Adaptations to Resistance Exercise and Training

Interrelationships between energy balance and postpartum reproductive function in dairy cattle.

To examine endogenous anabolic hormone and growth factor responses to various heavy resistance exercise protocols (HREPs), nine male subjects performed each of six randomly assigned HREPs, which consisted of identically ordered exercises carefully designed to control for load [5 vs. 10 repetitions maximum (RM)], rest period length (1 vs. 3 min), and total work effects. Serum human growth hormone (hGH), testosterone (T), somatomedin-C (SM-C), glucose, and whole blood lactate (HLa) concentrations were determined preexercise, midexercise (i.e., after 4 of 8 exercises), and at 0, 5, 15, 30, 60, 90, and 120 min postexercise. All HREPs produced significant (P less than 0.05) temporal increases in serum T concentrations, although the magnitude and time point of occurrence above resting values varied across HREPs. No differences were observed for T when integrated areas under the curve (AUCs) were compared. Although not all HREPs produced increases in serum hGH, the highest responses were observed consequent to the H10/1 exercise protocol (high total work, 1 min rest, 10-RM load) for both temporal and time integrated (AUC) responses. The pattern of SM-C increases varied among HREPs and did not consistently follow hGH changes. Whereas temporal changes were observed, no integrated time (AUC) differences between exercise protocols occurred. These data indicate that the release patterns (temporal or time integrated) observed are complex functions of the type of HREPs utilized and the physiological mechanisms involved with determining peripheral circulatory concentrations (e.g., clearance rates, transport, receptor binding). All HREPs may not affect muscle and connective tissue growth in the same manner because of possible differences in hormonal and growth factor release.

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Hormonal and growth factor responses to heavy resistance exercise protocols.

Risk factors for post partum ovarian dysfunction in high producing dairy cows in Belgium: a field study.

For tall fescue (Festuca arundinacea Schreb.) in the southeastern USA, persistence and yield are directly related to infection with a fungal endophyte [Neotyphodium coenophialum (Morgan-Jones & Gams.) Glenn, Bacon, & Hanlin comb, nov.]. However, most endophyte-infected (E+) tall fescue cultivars produce toxic ergot alkaloids resulting in poor weight gain and reproduction in grazing livestock. The objective of this paper was to assess the strategy of reinfecting 'Jesup' and 'Georgia 5' tall fescue with non-ergot alkaloid-producing endophyte strains. Different cultivar-strain combinations were tested against the E+ and endophyte-free (E-) versions of the same cultivars for stand survival and dry matter yield; in separate experiments, they were assessed for toxicity in lambs (Ovis aries). Most cultivar-strain combinations produced no ergot alkaloids but varied in ability to transmit through seed. The best combination, Jesup (AR542), possessed yield and stand survival better (P < 0.05) than the E- checks and equivalent (P < 0.05) to the E+ checks. Lambs gained an average of 124 g/d on both cultivars containing AR542, which was equivalent to gains on E- forage but approximately 57% greater than gains on E+ forage. Animals consuming forage from E- or non-ergot-producing strains did not exhibit depressed serum prolactin or elevated body temperatures of animals on E+ forage. The strategy of reinfecting tall fescue cultivars with naturally occurring, non-ergot-producing endophytes appears promising for removing toxicity symptoms and retaining agronomic performance, but intense screening is needed to identify the best cultivar-strain combinations.

Reinfection of Tall Fescue Cultivars with Non-Ergot Alkaloid–Producing Endophytes

Fescue toxicosis in livestock is due to ingestion of endophyte (Acremonium coenophialum) -infected tall fescue. Understanding mechanisms responsible for decreased calving and growth rates, delayed onset of puberty, and impaired function of corpora lutea in heifers at puberty consuming endophyte-infected fescue is an emerging field in reproductive toxicology. The condition decreases overall productivity through a reduction in reproductive efficiency, reduced weight gains, and lowered milk production. Reproduction in cattle may be further compromised by winter coat retention, increased susceptibility to high environmental temperatures, and light intolerance. Endocrine effects in steers associated with infected tall fescue include reduced prolactin and melatonin secretions and altered neurotransmitter metabolism in the hypothalamus, the pituitary, and pineal glands. Ewes have decreased prolactin and lengthened intervals from introduction of the ram until conception. The endophyte induces prolonged gestation, thickened placentas, large, weak foals, dystocia, and agalactia in pregnant mares. Ergot peptide alkaloids, produced by the endophyte, are suggested as the primary cause of fescue toxicosis. These compounds reduce prolactin, increase body temperatures, and have powerful vasoconstrictive effects. Neurohormonal imbalances of prolactin and melatonin, with restricted blood flow to internal organs, may be the principal causes of aberrant reproduction, growth, and maturation in livestock consuming endophyte-infected tall fescue.

Effects of fescue toxicosis on reproduction in livestock.

The metabolic consequences of stress: targets for stress and priorities of nutrient use.

To determine if a sex difference exists in the androgen response to heavy-resistance exercise, serum testosterone (T) and androstenedione (A) concentrations were measured in 20 men and 20 women before and during a 2-h period following 30 min of weight lifting. Hormone concentrations from venous blood samples were determined by radioimmunoassay. Prior to weight lifting, T for men (3.51±0.24 ng·ml−1) was approximately 10 times that for women (0.36±0.04 ng·ml−1), whereas A for women (1.26±0.07 ng·ml−1) was 43% higher than for men (0.88±0.07 ng·ml−1). Immediately following weight lifting, T was increased significantly (p<0.01) in men (0.76 ng·ml−1, 21.6%), but nonsignificantly in women (0.06 ng·ml−1, 16.7%). Resting T levels were restored within 30 min. Serum A levels decreased significantly (p<0.01) below pre-exercise levels at 2 h post-exercise for both men and women. It was concluded that men have a greater absolute T response to weight lifting than women, whereas the absolute A response to weight lifting is similar in men and women.

Comparison of serum testosterone and androstenedione responses to weight lifting in men and women.

Ergot alkaloids cause fescue toxicosis when livestock graze endophyte-infected tall fescue. It is generally accepted that ergovaline is the toxic component of endophyte-infected tall fescue, but there is no direct evidence to support this hypothesis. The objective of this study was to examine relative and potential transport of ergoline and ergopeptine alkaloids across isolated gastric tissues in vitro. Sheep ruminal and omasal tissues were surgically removed and placed in parabiotic chambers. Equimolar concentrations of lysergic acid, lysergol, ergonovine, ergotamine, and ergocryptine were added to a Kreb's Ringer phosphate (KRP) solution on the mucosal side of the tissue. Tissue was incubated in near-physiological conditions for 240 min. Samples were taken from KRP on the serosal side of the chambers at times 0, 30, 60, 120, 180, and 240 min and analyzed for ergot alkaloids by competitive ELISA. The serosal KRP remaining after incubation was freeze-dried and the alkaloid species quantified by HPLC. The area of ruminal and omasal tissues was measured and the potential transportable alkaloids calculated by multiplying the moles of transported alkaloids per square centimeter of each tissue type by the surface area of the tissue. Studies were conducted to compare alkaloid transport in reticular, ruminal, and omasal tissues and to determine whether transport was active or passive. Ruminal tissue had greater ergot alkaloid transport potential than omasal tissue (85 vs 60 mmol) because of a larger surface area. The ruminal posterior dorsal sac had the greatest potential for alkaloid transport, but the other ruminal tissues were not different from one another. Alkaloid transport was less among reticular tissues than among ruminal tissues. Transport of alkaloids seemed to be an active process. The alkaloids with greatest transport potential were lysergic acid and lysergol. Ergopeptine alkaloids tended to pass across omasal tissues in greater quantities than across ruminal tissues, but their transport was minimal compared to lysergic acid and lysergol.

Frederick N. Thompson

Papers

Reinfection of Tall Fescue Cultivars with Non-Ergot Alkaloid–Producing Endophytes

Effects of fescue toxicosis on reproduction in livestock.

The metabolic consequences of stress: targets for stress and priorities of nutrient use.

Comparison of serum testosterone and androstenedione responses to weight lifting in men and women.

Ergot alkaloid transport across ruminant gastric tissues